Move gitbook source code to es6 (linted)

294 files changed, 2775 insertions, 2813 deletions

diff --git a/package.json b/package.json
index 878eaa8..5940776 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "private": true,
   "devDependencies": {
-    "eslint": "2.10.2",
+    "eslint": "3.4.0",
     "eslint-config-gitbook": "^1.2.0",
     "expect": "^1.20.1",
     "lerna": "2.0.0-beta.26",
diff --git a/packages/gitbook/lib/cli/getBook.js b/packages/gitbook/lib/cli/getBook.js
deleted file mode 100644
index ac82187..0000000
--- a/packages/gitbook/lib/cli/getBook.js
+++ /dev/null
@@ -1,23 +0,0 @@
-var path = require('path');
-var Book = require('../models/book');
-var createNodeFS = require('../fs/node');
-
-/**
-    Return a book instance to work on from
-    command line args/kwargs
-
-    @param {Array} args
-    @param {Object} kwargs
-    @return {Book}
-*/
-function getBook(args, kwargs) {
-    var input = path.resolve(args[0] || process.cwd());
-    var logLevel = kwargs.log;
-
-    var fs = createNodeFS(input);
-    var book = Book.createForFS(fs);
-
-    return book.setLogLevel(logLevel);
-}
-
-module.exports = getBook;
diff --git a/packages/gitbook/lib/cli/getOutputFolder.js b/packages/gitbook/lib/cli/getOutputFolder.js
deleted file mode 100644
index 272dff9..0000000
--- a/packages/gitbook/lib/cli/getOutputFolder.js
+++ /dev/null
@@ -1,17 +0,0 @@
-var path = require('path');
-
-/**
-    Return path to output folder
-
-    @param {Array} args
-    @return {String}
-*/
-function getOutputFolder(args) {
-    var bookRoot = path.resolve(args[0] || process.cwd());
-    var defaultOutputRoot = path.join(bookRoot, '_book');
-    var outputFolder = args[1]? path.resolve(process.cwd(), args[1]) : defaultOutputRoot;
-
-    return outputFolder;
-}
-
-module.exports = getOutputFolder;
diff --git a/packages/gitbook/lib/cli/init.js b/packages/gitbook/lib/cli/init.js
deleted file mode 100644
index 55f1b15..0000000
--- a/packages/gitbook/lib/cli/init.js
+++ /dev/null
@@ -1,17 +0,0 @@
-var path = require('path');
-
-var options = require('./options');
-var initBook = require('../init');
-
-module.exports = {
-    name: 'init [book]',
-    description: 'setup and create files for chapters',
-    options: [
-        options.log
-    ],
-    exec: function(args, kwargs) {
-        var bookRoot = path.resolve(process.cwd(), args[0] || './');
-
-        return initBook(bookRoot);
-    }
-};
diff --git a/packages/gitbook/lib/cli/server.js b/packages/gitbook/lib/cli/server.js
deleted file mode 100644
index 752f867..0000000
--- a/packages/gitbook/lib/cli/server.js
+++ /dev/null
@@ -1,128 +0,0 @@
-var events = require('events');
-var http = require('http');
-var send = require('send');
-var util = require('util');
-var url = require('url');
-
-var Promise = require('../utils/promise');
-
-function Server() {
-    this.running = null;
-    this.dir = null;
-    this.port = 0;
-    this.sockets = [];
-}
-util.inherits(Server, events.EventEmitter);
-
-/**
-    Return true if the server is running
-
-    @return {Boolean}
-*/
-Server.prototype.isRunning = function() {
-    return !!this.running;
-};
-
-/**
-    Stop the server
-
-    @return {Promise}
-*/
-Server.prototype.stop = function() {
-    var that = this;
-    if (!this.isRunning()) return Promise();
-
-    var d = Promise.defer();
-    this.running.close(function(err) {
-        that.running = null;
-        that.emit('state', false);
-
-        if (err) d.reject(err);
-        else d.resolve();
-    });
-
-    for (var i = 0; i < this.sockets.length; i++) {
-        this.sockets[i].destroy();
-    }
-
-    return d.promise;
-};
-
-/**
-    Start the server
-
-    @return {Promise}
-*/
-Server.prototype.start = function(dir, port) {
-    var that = this, pre = Promise();
-    port = port || 8004;
-
-    if (that.isRunning()) pre = this.stop();
-    return pre
-    .then(function() {
-        var d = Promise.defer();
-
-        that.running = http.createServer(function(req, res){
-            // Render error
-            function error(err) {
-                res.statusCode = err.status || 500;
-                res.end(err.message);
-            }
-
-            // Redirect to directory's index.html
-            function redirect() {
-                var resultURL = urlTransform(req.url, function(parsed) {
-                    parsed.pathname += '/';
-                    return parsed;
-                });
-
-                res.statusCode = 301;
-                res.setHeader('Location', resultURL);
-                res.end('Redirecting to ' + resultURL);
-            }
-
-            res.setHeader('X-Current-Location', req.url);
-
-            // Send file
-            send(req, url.parse(req.url).pathname, {
-                root: dir
-            })
-            .on('error', error)
-            .on('directory', redirect)
-            .pipe(res);
-        });
-
-        that.running.on('connection', function (socket) {
-            that.sockets.push(socket);
-            socket.setTimeout(4000);
-            socket.on('close', function () {
-                that.sockets.splice(that.sockets.indexOf(socket), 1);
-            });
-        });
-
-        that.running.listen(port, function(err) {
-            if (err) return d.reject(err);
-
-            that.port = port;
-            that.dir = dir;
-            that.emit('state', true);
-            d.resolve();
-        });
-
-        return d.promise;
-    });
-};
-
-/**
-    urlTransform is a helper function that allows a function to transform
-    a url string in it's parsed form and returns the new url as a string
-
-    @param {String} uri
-    @param {Function} fn
-    @return {String}
-*/
-function urlTransform(uri, fn) {
-    return url.format(fn(url.parse(uri)));
-}
-
-module.exports = Server;
diff --git a/packages/gitbook/lib/constants/configDefault.js b/packages/gitbook/lib/constants/configDefault.js
deleted file mode 100644
index 0d95883..0000000
--- a/packages/gitbook/lib/constants/configDefault.js
+++ /dev/null
@@ -1,6 +0,0 @@
-var Immutable = require('immutable');
-var jsonSchemaDefaults = require('json-schema-defaults');
-
-var schema = require('./configSchema');
-
-module.exports = Immutable.fromJS(jsonSchemaDefaults(schema));
diff --git a/packages/gitbook/lib/json/encodeBook.js b/packages/gitbook/lib/json/encodeBook.js
deleted file mode 100644
index 9d7ec77..0000000
--- a/packages/gitbook/lib/json/encodeBook.js
+++ /dev/null
@@ -1,39 +0,0 @@
-var extend = require('extend');
-
-var gitbook = require('../gitbook');
-var encodeSummary = require('./encodeSummary');
-var encodeGlossary = require('./encodeGlossary');
-var encodeReadme = require('./encodeReadme');
-var encodeLanguages = require('./encodeLanguages');
-
-/**
-    Encode a book to JSON
-
-    @param {Book}
-    @return {Object}
-*/
-function encodeBookToJson(book) {
-    var config = book.getConfig();
-    var language = book.getLanguage();
-
-    var variables = config.getValue('variables', {});
-
-    return {
-        summary: encodeSummary(book.getSummary()),
-        glossary: encodeGlossary(book.getGlossary()),
-        readme: encodeReadme(book.getReadme()),
-        config: book.getConfig().getValues().toJS(),
-
-        languages: book.isMultilingual()? encodeLanguages(book.getLanguages()) : undefined,
-
-        gitbook: {
-            version: gitbook.version,
-            time: gitbook.START_TIME
-        },
-        book: extend({
-            language: language? language : undefined
-        }, variables.toJS())
-    };
-}
-
-module.exports = encodeBookToJson;
diff --git a/packages/gitbook/lib/output/createTemplateEngine.js b/packages/gitbook/lib/output/createTemplateEngine.js
deleted file mode 100644
index 8cf320e..0000000
--- a/packages/gitbook/lib/output/createTemplateEngine.js
+++ /dev/null
@@ -1,45 +0,0 @@
-var Templating = require('../templating');
-var TemplateEngine = require('../models/templateEngine');
-
-var Api = require('../api');
-var Plugins = require('../plugins');
-
-var defaultBlocks = require('../constants/defaultBlocks');
-var defaultFilters = require('../constants/defaultFilters');
-
-/**
-    Create template engine for an output.
-    It adds default filters/blocks, then add the ones from plugins
-
-    @param {Output} output
-    @return {TemplateEngine}
-*/
-function createTemplateEngine(output) {
-    var plugins = output.getPlugins();
-    var book = output.getBook();
-    var rootFolder = book.getContentRoot();
-    var logger = book.getLogger();
-
-    var filters = Plugins.listFilters(plugins);
-    var blocks = Plugins.listBlocks(plugins);
-
-    // Extend with default
-    blocks = defaultBlocks.merge(blocks);
-    filters = defaultFilters.merge(filters);
-
-    // Create loader
-    var transformFn = Templating.replaceShortcuts.bind(null, blocks);
-    var loader = new Templating.ConrefsLoader(rootFolder, transformFn, logger);
-
-    // Create API context
-    var context = Api.encodeGlobal(output);
-
-    return new TemplateEngine({
-        filters:    filters,
-        blocks:     blocks,
-        loader:     loader,
-        context:    context
-    });
-}
-
-module.exports = createTemplateEngine;
diff --git a/packages/gitbook/lib/output/modifiers/__tests__/fetchRemoteImages.js b/packages/gitbook/lib/output/modifiers/__tests__/fetchRemoteImages.js
deleted file mode 100644
index bc1704d..0000000
--- a/packages/gitbook/lib/output/modifiers/__tests__/fetchRemoteImages.js
+++ /dev/null
@@ -1,40 +0,0 @@
-var cheerio = require('cheerio');
-var tmp = require('tmp');
-var path = require('path');
-
-var URL = 'https://upload.wikimedia.org/wikipedia/commons/thumb/4/47/PNG_transparency_demonstration_1.png/280px-PNG_transparency_demonstration_1.png';
-
-describe('fetchRemoteImages', function() {
-    var dir;
-    var fetchRemoteImages = require('../fetchRemoteImages');
-
-    beforeEach(function() {
-        dir = tmp.dirSync();
-    });
-
-    it('should download image file', function() {
-        var $ = cheerio.load('<img src="' + URL + '" />');
-
-        return fetchRemoteImages(dir.name, 'index.html', $)
-        .then(function() {
-            var $img = $('img');
-            var src = $img.attr('src');
-
-            expect(dir.name).toHaveFile(src);
-        });
-    });
-
-    it('should download image file and replace with relative path', function() {
-        var $ = cheerio.load('<img src="' + URL + '" />');
-
-        return fetchRemoteImages(dir.name, 'test/index.html', $)
-        .then(function() {
-            var $img = $('img');
-            var src = $img.attr('src');
-
-            expect(dir.name).toHaveFile(path.join('test', src));
-        });
-    });
-});
-
-
diff --git a/packages/gitbook/lib/output/modifiers/__tests__/inlinePng.js b/packages/gitbook/lib/output/modifiers/__tests__/inlinePng.js
deleted file mode 100644
index 0073cff..0000000
--- a/packages/gitbook/lib/output/modifiers/__tests__/inlinePng.js
+++ /dev/null
@@ -1,25 +0,0 @@
-var cheerio = require('cheerio');
-var tmp = require('tmp');
-var inlinePng = require('../inlinePng');
-
-describe('inlinePng', function() {
-    var dir;
-
-    beforeEach(function() {
-        dir = tmp.dirSync();
-    });
-
-    it('should write an inline PNG using data URI as a file', function() {
-        var $ = cheerio.load('<img alt="GitBook Logo 20x20" src="data:image/png;base64,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"/>');
-
-        return inlinePng(dir.name, 'index.html', $)
-        .then(function() {
-            var $img = $('img');
-            var src = $img.attr('src');
-
-            expect(dir.name).toHaveFile(src);
-        });
-    });
-});
-
-
diff --git a/packages/gitbook/lib/output/modifiers/__tests__/svgToImg.js b/packages/gitbook/lib/output/modifiers/__tests__/svgToImg.js
deleted file mode 100644
index 5fe9796..0000000
--- a/packages/gitbook/lib/output/modifiers/__tests__/svgToImg.js
+++ /dev/null
@@ -1,25 +0,0 @@
-var cheerio = require('cheerio');
-var tmp = require('tmp');
-
-describe('svgToImg', function() {
-    var dir;
-    var svgToImg = require('../svgToImg');
-
-    beforeEach(function() {
-        dir = tmp.dirSync();
-    });
-
-    it('should write svg as a file', function() {
-        var $ = cheerio.load('<svg xmlns="http://www.w3.org/2000/svg" width="200" height="100" version="1.1"><rect width="200" height="100" stroke="black" stroke-width="6" fill="green"/></svg>');
-
-        return svgToImg(dir.name, 'index.html', $)
-        .then(function() {
-            var $img = $('img');
-            var src = $img.attr('src');
-
-            expect(dir.name).toHaveFile(src);
-        });
-    });
-});
-
-
diff --git a/packages/gitbook/lib/output/modifiers/__tests__/svgToPng.js b/packages/gitbook/lib/output/modifiers/__tests__/svgToPng.js
deleted file mode 100644
index dbb3502..0000000
--- a/packages/gitbook/lib/output/modifiers/__tests__/svgToPng.js
+++ /dev/null
@@ -1,33 +0,0 @@
-var cheerio = require('cheerio');
-var tmp = require('tmp');
-var path = require('path');
-
-var svgToImg = require('../svgToImg');
-var svgToPng = require('../svgToPng');
-
-describe('svgToPng', function() {
-    var dir;
-
-    beforeEach(function() {
-        dir = tmp.dirSync();
-    });
-
-    it('should write svg as png file', function() {
-        var $ = cheerio.load('<svg xmlns="http://www.w3.org/2000/svg" width="200" height="100" version="1.1"><rect width="200" height="100" stroke="black" stroke-width="6" fill="green"/></svg>');
-        var fileName = 'index.html';
-
-        return svgToImg(dir.name, fileName, $)
-        .then(function() {
-            return svgToPng(dir.name, fileName, $);
-        })
-        .then(function() {
-            var $img = $('img');
-            var src = $img.attr('src');
-
-            expect(dir.name).toHaveFile(src);
-            expect(path.extname(src)).toBe('.png');
-        });
-    });
-});
-
-
diff --git a/packages/gitbook/lib/output/website/onFinish.js b/packages/gitbook/lib/output/website/onFinish.js
deleted file mode 100644
index 5267458..0000000
--- a/packages/gitbook/lib/output/website/onFinish.js
+++ /dev/null
@@ -1,35 +0,0 @@
-var Promise = require('../../utils/promise');
-var JSONUtils = require('../../json');
-var Templating = require('../../templating');
-var writeFile = require('../helper/writeFile');
-var createTemplateEngine = require('./createTemplateEngine');
-
-/**
-    Finish the generation, write the languages index
-
-    @param {Output}
-    @return {Output}
-*/
-function onFinish(output) {
-    var book = output.getBook();
-    var options = output.getOptions();
-    var prefix = options.get('prefix');
-
-    if (!book.isMultilingual()) {
-        return Promise(output);
-    }
-
-    var filePath = 'index.html';
-    var engine = createTemplateEngine(output, filePath);
-    var context = JSONUtils.encodeOutput(output);
-
-    // Render the theme
-    return Templating.renderFile(engine, prefix + '/languages.html', context)
-
-    // Write it to the disk
-    .then(function(tplOut) {
-        return writeFile(output, filePath, tplOut.getContent());
-    });
-}
-
-module.exports = onFinish;
diff --git a/packages/gitbook/lib/plugins/__tests__/installPlugin.js b/packages/gitbook/lib/plugins/__tests__/installPlugin.js
deleted file mode 100644
index 0c1a346..0000000
--- a/packages/gitbook/lib/plugins/__tests__/installPlugin.js
+++ /dev/null
@@ -1,29 +0,0 @@
-var path = require('path');
-
-var PluginDependency = require('../../models/pluginDependency');
-var Book = require('../../models/book');
-var NodeFS = require('../../fs/node');
-var installPlugin = require('../installPlugin');
-
-var Parse = require('../../parse');
-
-describe('installPlugin', function() {
-    var book;
-
-    this.timeout(30000);
-
-    before(function() {
-        var fs = NodeFS(path.resolve(__dirname, '../../../'));
-        var baseBook = Book.createForFS(fs);
-
-        return Parse.parseConfig(baseBook)
-        .then(function(_book) {
-            book = _book;
-        });
-    });
-
-    it('must install a plugin from NPM', function() {
-        var dep = PluginDependency.createFromString('ga');
-        return installPlugin(book, dep);
-    });
-});
diff --git a/packages/gitbook/lib/plugins/locateRootFolder.js b/packages/gitbook/lib/plugins/locateRootFolder.js
deleted file mode 100644
index 1139510..0000000
--- a/packages/gitbook/lib/plugins/locateRootFolder.js
+++ /dev/null
@@ -1,22 +0,0 @@
-var path = require('path');
-var resolve = require('resolve');
-
-var DEFAULT_PLUGINS = require('../constants/defaultPlugins');
-
-/**
- * Resolve the root folder containing for node_modules
- * since gitbook can be used as a library and dependency can be flattened.
- *
- * @return {String} folderPath
- */
-function locateRootFolder() {
-    var firstDefaultPlugin = DEFAULT_PLUGINS.first();
-    var pluginPath = resolve.sync(firstDefaultPlugin.getNpmID() + '/package.json', {
-        basedir: __dirname
-    });
-    var nodeModules = path.resolve(pluginPath, '../../..');
-
-    return nodeModules;
-}
-
-module.exports = locateRootFolder;
diff --git a/packages/gitbook/lib/utils/git.js b/packages/gitbook/lib/utils/git.js
deleted file mode 100644
index 6884b83..0000000
--- a/packages/gitbook/lib/utils/git.js
+++ /dev/null
@@ -1,133 +0,0 @@
-var is = require('is');
-var path = require('path');
-var crc = require('crc');
-var URI = require('urijs');
-
-var pathUtil = require('./path');
-var Promise = require('./promise');
-var command = require('./command');
-var fs = require('./fs');
-
-var GIT_PREFIX = 'git+';
-
-function Git() {
-    this.tmpDir;
-    this.cloned = {};
-}
-
-// Return an unique ID for a combinaison host/ref
-Git.prototype.repoID = function(host, ref) {
-    return crc.crc32(host+'#'+(ref || '')).toString(16);
-};
-
-// Allocate a temporary folder for cloning repos in it
-Git.prototype.allocateDir = function() {
-    var that = this;
-
-    if (this.tmpDir) return Promise();
-
-    return fs.tmpDir()
-    .then(function(dir) {
-        that.tmpDir = dir;
-    });
-};
-
-// Clone a git repository if non existant
-Git.prototype.clone = function(host, ref) {
-    var that = this;
-
-    return this.allocateDir()
-
-    // Return or clone the git repo
-    .then(function() {
-        // Unique ID for repo/ref combinaison
-        var repoId = that.repoID(host, ref);
-
-        // Absolute path to the folder
-        var repoPath = path.join(that.tmpDir, repoId);
-
-        if (that.cloned[repoId]) return repoPath;
-
-        // Clone repo
-        return command.exec('git clone '+host+' '+repoPath)
-
-        // Checkout reference if specified
-        .then(function() {
-            that.cloned[repoId] = true;
-
-            if (!ref) return;
-            return command.exec('git checkout '+ref, { cwd: repoPath });
-        })
-        .thenResolve(repoPath);
-    });
-};
-
-// Get file from a git repo
-Git.prototype.resolve = function(giturl) {
-    // Path to a file in a git repo?
-    if (!Git.isUrl(giturl)) {
-        if (this.resolveRoot(giturl)) return Promise(giturl);
-        return Promise(null);
-    }
-    if (is.string(giturl)) giturl = Git.parseUrl(giturl);
-    if (!giturl) return Promise(null);
-
-    // Clone or get from cache
-    return this.clone(giturl.host, giturl.ref)
-    .then(function(repo) {
-        return path.resolve(repo, giturl.filepath);
-    });
-};
-
-// Return root of git repo from a filepath
-Git.prototype.resolveRoot = function(filepath) {
-    var relativeToGit, repoId;
-
-    // No git repo cloned, or file is not in a git repository
-    if (!this.tmpDir || !pathUtil.isInRoot(this.tmpDir, filepath)) return null;
-
-    // Extract first directory (is the repo id)
-    relativeToGit = path.relative(this.tmpDir, filepath);
-    repoId = relativeToGit.split(path.sep)[0];
-    if (!repoId) {
-        return;
-    }
-
-    // Return an absolute file
-    return path.resolve(this.tmpDir, repoId);
-};
-
-// Check if an url is a git dependency url
-Git.isUrl = function(giturl) {
-    return (giturl.indexOf(GIT_PREFIX) === 0);
-};
-
-// Parse and extract infos
-Git.parseUrl = function(giturl) {
-    var ref, uri, fileParts, filepath;
-
-    if (!Git.isUrl(giturl)) return null;
-    giturl = giturl.slice(GIT_PREFIX.length);
-
-    uri = new URI(giturl);
-    ref = uri.fragment() || null;
-    uri.fragment(null);
-
-    // Extract file inside the repo (after the .git)
-    fileParts = uri.path().split('.git');
-    filepath = fileParts.length > 1? fileParts.slice(1).join('.git') : '';
-    if (filepath[0] == '/') {
-        filepath = filepath.slice(1);
-    }
-
-    // Recreate pathname without the real filename
-    uri.path(fileParts[0] + '.git');
-
-    return {
-        host: uri.toString(),
-        ref: ref,
-        filepath: filepath
-    };
-};
-
-module.exports = Git;
diff --git a/packages/gitbook/lib/__tests__/gitbook.js b/packages/gitbook/src/__tests__/gitbook.js
index c3669bb..5292e01 100644
--- a/packages/gitbook/lib/__tests__/gitbook.js
+++ b/packages/gitbook/src/__tests__/gitbook.js
@@ -1,4 +1,4 @@
-var gitbook = require('../gitbook');
+const gitbook = require('../gitbook');
 
 describe('satisfies', function() {
 
diff --git a/packages/gitbook/lib/__tests__/init.js b/packages/gitbook/src/__tests__/init.js
index 66188a3..d8e5398 100644
--- a/packages/gitbook/lib/__tests__/init.js
+++ b/packages/gitbook/src/__tests__/init.js
@@ -1,10 +1,10 @@
-var tmp = require('tmp');
-var initBook = require('../init');
+const tmp = require('tmp');
+const initBook = require('../init');
 
 describe('initBook', function() {
 
     it('should create a README and SUMMARY for empty book', function() {
-        var dir = tmp.dirSync();
+        const dir = tmp.dirSync();
 
         return initBook(dir.name)
         .then(function() {
diff --git a/packages/gitbook/lib/__tests__/module.js b/packages/gitbook/src/__tests__/module.js
index d9220f5..d9220f5 100644
--- a/packages/gitbook/lib/__tests__/module.js
+++ b/packages/gitbook/src/__tests__/module.js
diff --git a/packages/gitbook/lib/api/decodeConfig.js b/packages/gitbook/src/api/decodeConfig.js
index 5e00df5..0c5ba66 100644
--- a/packages/gitbook/lib/api/decodeConfig.js
+++ b/packages/gitbook/src/api/decodeConfig.js
@@ -6,7 +6,7 @@
     @return {Config}
 */
 function decodeGlobal(config, result) {
-    var values = result.values;
+    const values = result.values;
 
     delete values.generator;
     delete values.output;
diff --git a/packages/gitbook/lib/api/decodeGlobal.js b/packages/gitbook/src/api/decodeGlobal.js
index 118afb2..063683a 100644
--- a/packages/gitbook/lib/api/decodeGlobal.js
+++ b/packages/gitbook/src/api/decodeGlobal.js
@@ -1,4 +1,4 @@
-var decodeConfig = require('./decodeConfig');
+const decodeConfig = require('./decodeConfig');
 
 /**
     Decode changes from a JS API to a output object.
@@ -9,8 +9,8 @@ var decodeConfig = require('./decodeConfig');
     @return {Output}
 */
 function decodeGlobal(output, result) {
-    var book = output.getBook();
-    var config = book.getConfig();
+    let book = output.getBook();
+    let config = book.getConfig();
 
     // Update config
     config = decodeConfig(config, result.config);
diff --git a/packages/gitbook/lib/api/decodePage.js b/packages/gitbook/src/api/decodePage.js
index c85dd1b..4fd78af 100644
--- a/packages/gitbook/lib/api/decodePage.js
+++ b/packages/gitbook/src/api/decodePage.js
@@ -1,4 +1,4 @@
-var deprecate = require('./deprecate');
+const deprecate = require('./deprecate');
 
 /**
     Decode changes from a JS API to a page object.
@@ -10,7 +10,7 @@ var deprecate = require('./deprecate');
     @return {Page}
 */
 function decodePage(output, page, result) {
-    var originalContent = page.getContent();
+    const originalContent = page.getContent();
 
     // No returned value
     // Existing content will be used
diff --git a/packages/gitbook/lib/api/deprecate.js b/packages/gitbook/src/api/deprecate.js
index 7a93a91..879355c 100644
--- a/packages/gitbook/lib/api/deprecate.js
+++ b/packages/gitbook/src/api/deprecate.js
@@ -1,8 +1,8 @@
-var is = require('is');
-var objectPath = require('object-path');
+const is = require('is');
+const objectPath = require('object-path');
 
-var logged = {};
-var disabled = {};
+const logged = {};
+const disabled = {};
 
 /**
     Log a deprecated notice
@@ -16,7 +16,7 @@ function logNotice(book, key, message) {
 
     logged[key] = true;
 
-    var logger = book.getLogger();
+    const logger = book.getLogger();
     logger.warn.ln(message);
 }
 
@@ -48,22 +48,22 @@ function deprecateMethod(book, key, fn, msg) {
     @return {Function}
 */
 function deprecateField(book, key, instance, property, value, msg) {
-    var store = undefined;
+    let store = undefined;
 
-    var prepare = function() {
+    const prepare = function() {
         if (!is.undefined(store)) return;
 
         if (is.fn(value)) store = value();
         else store = value;
     };
 
-    var getter = function(){
+    const getter = function() {
         prepare();
 
         logNotice(book, key, msg);
         return store;
     };
-    var setter = function(v) {
+    const setter = function(v) {
         prepare();
 
         logNotice(book, key, msg);
@@ -108,7 +108,7 @@ function disableDeprecation(key) {
 */
 function deprecateRenamedMethod(book, key, instance, oldName, newName, msg) {
     msg = msg || ('"' + oldName + '" is deprecated, use "' + newName + '()" instead');
-    var fn = objectPath.get(instance, newName);
+    const fn = objectPath.get(instance, newName);
 
     instance[oldName] = deprecateMethod(book, key, fn, msg);
 }
diff --git a/packages/gitbook/lib/api/encodeConfig.js b/packages/gitbook/src/api/encodeConfig.js
index 2a05528..096f136 100644
--- a/packages/gitbook/lib/api/encodeConfig.js
+++ b/packages/gitbook/src/api/encodeConfig.js
@@ -1,5 +1,5 @@
-var objectPath = require('object-path');
-var deprecate = require('./deprecate');
+const objectPath = require('object-path');
+const deprecate = require('./deprecate');
 
 /**
     Encode a config object into a JS config api
@@ -9,14 +9,14 @@ var deprecate = require('./deprecate');
     @return {Object}
 */
 function encodeConfig(output, config) {
-    var result = {
+    const result = {
         values: config.getValues().toJS(),
 
-        get: function(key, defaultValue) {
+        get(key, defaultValue) {
             return objectPath.get(result.values, key, defaultValue);
         },
 
-        set: function(key, value) {
+        set(key, value) {
             return objectPath.set(result.values, key, value);
         }
     };
diff --git a/packages/gitbook/lib/api/encodeGlobal.js b/packages/gitbook/src/api/encodeGlobal.js
index a366526..21a1e73 100644
--- a/packages/gitbook/lib/api/encodeGlobal.js
+++ b/packages/gitbook/src/api/encodeGlobal.js
@@ -1,19 +1,19 @@
-var path = require('path');
-var Promise = require('../utils/promise');
-var PathUtils = require('../utils/path');
-var fs = require('../utils/fs');
-
-var Plugins = require('../plugins');
-var deprecate = require('./deprecate');
-var fileToURL = require('../output/helper/fileToURL');
-var defaultBlocks = require('../constants/defaultBlocks');
-var gitbook = require('../gitbook');
-var parsers = require('../parsers');
-
-var encodeConfig = require('./encodeConfig');
-var encodeSummary = require('./encodeSummary');
-var encodeNavigation = require('./encodeNavigation');
-var encodePage = require('./encodePage');
+const path = require('path');
+const Promise = require('../utils/promise');
+const PathUtils = require('../utils/path');
+const fs = require('../utils/fs');
+
+const Plugins = require('../plugins');
+const deprecate = require('./deprecate');
+const fileToURL = require('../output/helper/fileToURL');
+const defaultBlocks = require('../constants/defaultBlocks');
+const gitbook = require('../gitbook');
+const parsers = require('../parsers');
+
+const encodeConfig = require('./encodeConfig');
+const encodeSummary = require('./encodeSummary');
+const encodeNavigation = require('./encodeNavigation');
+const encodePage = require('./encodePage');
 
 /**
     Encode a global context into a JS object
@@ -23,14 +23,14 @@ var encodePage = require('./encodePage');
     @return {Object}
 */
 function encodeGlobal(output) {
-    var book = output.getBook();
-    var bookFS = book.getContentFS();
-    var logger = output.getLogger();
-    var outputFolder = output.getRoot();
-    var plugins = output.getPlugins();
-    var blocks = Plugins.listBlocks(plugins);
-
-    var result = {
+    const book = output.getBook();
+    const bookFS = book.getContentFS();
+    const logger = output.getLogger();
+    const outputFolder = output.getRoot();
+    const plugins = output.getPlugins();
+    const blocks = Plugins.listBlocks(plugins);
+
+    const result = {
         log: logger,
         config: encodeConfig(output, book.getConfig()),
         summary: encodeSummary(output, book.getSummary()),
@@ -40,7 +40,7 @@ function encodeGlobal(output) {
 
             @return {Boolean}
         */
-        isMultilingual: function() {
+        isMultilingual() {
             return book.isMultilingual();
         },
 
@@ -49,7 +49,7 @@ function encodeGlobal(output) {
 
             @return {Boolean}
         */
-        isLanguageBook: function() {
+        isLanguageBook() {
             return book.isLanguageBook();
         },
 
@@ -59,7 +59,7 @@ function encodeGlobal(output) {
             @param {String} fileName
             @return {Promise<Buffer>}
         */
-        readFile: function(fileName) {
+        readFile(fileName) {
             return bookFS.read(fileName);
         },
 
@@ -69,7 +69,7 @@ function encodeGlobal(output) {
             @param {String} fileName
             @return {Promise<String>}
         */
-        readFileAsString: function(fileName) {
+        readFileAsString(fileName) {
             return bookFS.readAsString(fileName);
         },
 
@@ -79,7 +79,7 @@ function encodeGlobal(output) {
             @param {String} fileName
             @return {String}
         */
-        resolve: function(fileName) {
+        resolve(fileName) {
             return path.resolve(book.getContentRoot(), fileName);
         },
 
@@ -89,8 +89,8 @@ function encodeGlobal(output) {
             @param {String} filePath
             @return {String}
         */
-        getPageByPath: function(filePath) {
-            var page = output.getPage(filePath);
+        getPageByPath(filePath) {
+            const page = output.getPage(filePath);
             if (!page) return undefined;
 
             return encodePage(output, page);
@@ -103,8 +103,8 @@ function encodeGlobal(output) {
             @param {String} text
             @return {Promise<String>}
         */
-        renderBlock: function(type, text) {
-            var parser = parsers.get(type);
+        renderBlock(type, text) {
+            const parser = parsers.get(type);
 
             return parser.parsePage(text)
                 .get('content');
@@ -117,14 +117,15 @@ function encodeGlobal(output) {
             @param {String} text
             @return {Promise<String>}
         */
-        renderInline: function(type, text) {
-            var parser = parsers.get(type);
+        renderInline(type, text) {
+            const parser = parsers.get(type);
 
             return parser.parseInline(text)
                 .get('content');
         },
 
         template: {
+
             /**
                 Apply a templating block and returns its result
 
@@ -132,13 +133,14 @@ function encodeGlobal(output) {
                 @param {Object} blockData
                 @return {Promise|Object}
             */
-            applyBlock: function(name, blockData) {
-                var block = blocks.get(name) || defaultBlocks.get(name);
+            applyBlock(name, blockData) {
+                const block = blocks.get(name) || defaultBlocks.get(name);
                 return Promise(block.applyBlock(blockData, result));
             }
         },
 
         output: {
+
             /**
                 Name of the generator being used
                 {String}
@@ -149,7 +151,7 @@ function encodeGlobal(output) {
                 Return absolute path to the root folder of output
                 @return {String}
             */
-            root: function() {
+            root() {
                 return outputFolder;
             },
 
@@ -159,7 +161,7 @@ function encodeGlobal(output) {
                 @param {String} fileName
                 @return {String}
             */
-            resolve: function(fileName) {
+            resolve(fileName) {
                 return path.resolve(outputFolder, fileName);
             },
 
@@ -167,7 +169,7 @@ function encodeGlobal(output) {
                 Convert a filepath into an url
                 @return {String}
             */
-            toURL: function(filePath) {
+            toURL(filePath) {
                 return fileToURL(output, filePath);
             },
 
@@ -177,10 +179,10 @@ function encodeGlobal(output) {
                 @param {String} fileName
                 @return {Promise}
             */
-            hasFile: function(fileName, content) {
+            hasFile(fileName, content) {
                 return Promise()
                 .then(function() {
-                    var filePath = PathUtils.resolveInRoot(outputFolder, fileName);
+                    const filePath = PathUtils.resolveInRoot(outputFolder, fileName);
 
                     return fs.exists(filePath);
                 });
@@ -194,10 +196,10 @@ function encodeGlobal(output) {
                 @param {Buffer} content
                 @return {Promise}
             */
-            writeFile: function(fileName, content) {
+            writeFile(fileName, content) {
                 return Promise()
                 .then(function() {
-                    var filePath = PathUtils.resolveInRoot(outputFolder, fileName);
+                    const filePath = PathUtils.resolveInRoot(outputFolder, fileName);
 
                     return fs.ensureFile(filePath)
                     .then(function() {
@@ -215,10 +217,10 @@ function encodeGlobal(output) {
                 @param {Buffer} content
                 @return {Promise}
             */
-            copyFile: function(inputFile, outputFile, content) {
+            copyFile(inputFile, outputFile, content) {
                 return Promise()
                 .then(function() {
-                    var outputFilePath = PathUtils.resolveInRoot(outputFolder, outputFile);
+                    const outputFilePath = PathUtils.resolveInRoot(outputFolder, outputFile);
 
                     return fs.ensureFile(outputFilePath)
                     .then(function() {
diff --git a/packages/gitbook/lib/api/encodeNavigation.js b/packages/gitbook/src/api/encodeNavigation.js
index 8e329a1..d54239d 100644
--- a/packages/gitbook/lib/api/encodeNavigation.js
+++ b/packages/gitbook/src/api/encodeNavigation.js
@@ -1,4 +1,4 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
 /**
     Encode an article for next/prev
@@ -8,7 +8,7 @@ var Immutable = require('immutable');
     @return {Object}
 */
 function encodeArticle(pages, article) {
-    var articlePath = article.getPath();
+    const articlePath = article.getPath();
 
     return {
         path: articlePath,
@@ -26,21 +26,21 @@ function encodeArticle(pages, article) {
     @return {Object}
 */
 function encodeNavigation(output) {
-    var book = output.getBook();
-    var pages = output.getPages();
-    var summary = book.getSummary();
-    var articles = summary.getArticlesAsList();
+    const book = output.getBook();
+    const pages = output.getPages();
+    const summary = book.getSummary();
+    const articles = summary.getArticlesAsList();
 
 
-    var navigation = articles
+    const navigation = articles
         .map(function(article, i) {
-            var ref = article.getRef();
+            const ref = article.getRef();
             if (!ref) {
                 return undefined;
             }
 
-            var prev = articles.get(i - 1);
-            var next = articles.get(i + 1);
+            const prev = articles.get(i - 1);
+            const next = articles.get(i + 1);
 
             return [
                 ref,
@@ -48,8 +48,8 @@ function encodeNavigation(output) {
                     index: i,
                     title: article.getTitle(),
                     introduction: (i === 0),
-                    prev: prev? encodeArticle(pages, prev) : undefined,
-                    next: next? encodeArticle(pages, next) : undefined,
+                    prev: prev ? encodeArticle(pages, prev) : undefined,
+                    next: next ? encodeArticle(pages, next) : undefined,
                     level: article.getLevel()
                 }
             ];
diff --git a/packages/gitbook/lib/api/encodePage.js b/packages/gitbook/src/api/encodePage.js
index 379d3d5..fb77fcd 100644
--- a/packages/gitbook/lib/api/encodePage.js
+++ b/packages/gitbook/src/api/encodePage.js
@@ -1,6 +1,6 @@
-var JSONUtils = require('../json');
-var deprecate = require('./deprecate');
-var encodeProgress = require('./encodeProgress');
+const JSONUtils = require('../json');
+const deprecate = require('./deprecate');
+const encodeProgress = require('./encodeProgress');
 
 /**
     Encode a page in a context to a JS API
@@ -10,13 +10,13 @@ var encodeProgress = require('./encodeProgress');
     @return {Object}
 */
 function encodePage(output, page) {
-    var book = output.getBook();
-    var summary = book.getSummary();
-    var fs = book.getContentFS();
-    var file = page.getFile();
+    const book = output.getBook();
+    const summary = book.getSummary();
+    const fs = book.getContentFS();
+    const file = page.getFile();
 
     // JS Page is based on the JSON output
-    var result = JSONUtils.encodePage(page, summary);
+    const result = JSONUtils.encodePage(page, summary);
 
     result.type = file.getType();
     result.path = file.getPath();
diff --git a/packages/gitbook/lib/api/encodeProgress.js b/packages/gitbook/src/api/encodeProgress.js
index afa0341..3224370 100644
--- a/packages/gitbook/lib/api/encodeProgress.js
+++ b/packages/gitbook/src/api/encodeProgress.js
@@ -1,5 +1,5 @@
-var Immutable = require('immutable');
-var encodeNavigation = require('./encodeNavigation');
+const Immutable = require('immutable');
+const encodeNavigation = require('./encodeNavigation');
 
 /**
     page.progress is a deprecated property from GitBook v2
@@ -9,15 +9,15 @@ var encodeNavigation = require('./encodeNavigation');
     @return {Object}
 */
 function encodeProgress(output, page) {
-    var current = page.getPath();
-    var navigation = encodeNavigation(output);
+    const current = page.getPath();
+    let navigation = encodeNavigation(output);
     navigation = Immutable.Map(navigation);
 
-    var n = navigation.size;
-    var percent = 0, prevPercent = 0, currentChapter = null;
-    var done = true;
+    const n = navigation.size;
+    let percent = 0, prevPercent = 0, currentChapter = null;
+    let done = true;
 
-    var chapters = navigation
+    const chapters = navigation
         .map(function(nav, chapterPath) {
             nav.path = chapterPath;
             return nav;
@@ -46,13 +46,13 @@ function encodeProgress(output, page) {
 
     return {
         // Previous percent
-        prevPercent: prevPercent,
+        prevPercent,
 
         // Current percent
-        percent: percent,
+        percent,
 
         // List of chapter with progress
-        chapters: chapters,
+        chapters,
 
         // Current chapter
         current: currentChapter
diff --git a/packages/gitbook/lib/api/encodeSummary.js b/packages/gitbook/src/api/encodeSummary.js
index 0d66ded..323f5d4 100644
--- a/packages/gitbook/lib/api/encodeSummary.js
+++ b/packages/gitbook/src/api/encodeSummary.js
@@ -1,4 +1,4 @@
-var encodeSummaryArticle = require('../json/encodeSummaryArticle');
+const encodeSummaryArticle = require('../json/encodeSummaryArticle');
 
 /**
     Encode summary to provide an API to plugin
@@ -8,15 +8,16 @@ var encodeSummaryArticle = require('../json/encodeSummaryArticle');
     @return {Object}
 */
 function encodeSummary(output, summary) {
-    var result = {
+    const result = {
+
         /**
             Iterate over the summary, it stops when the "iter" returns false
 
             @param {Function} iter
         */
-        walk: function (iter) {
+        walk(iter) {
             summary.getArticle(function(article) {
-                var jsonArticle = encodeSummaryArticle(article, false);
+                const jsonArticle = encodeSummaryArticle(article, false);
 
                 return iter(jsonArticle);
             });
@@ -28,9 +29,9 @@ function encodeSummary(output, summary) {
             @param {String} level
             @return {Object}
         */
-        getArticleByLevel: function(level) {
-            var article = summary.getByLevel(level);
-            return (article? encodeSummaryArticle(article) : undefined);
+        getArticleByLevel(level) {
+            const article = summary.getByLevel(level);
+            return (article ? encodeSummaryArticle(article) : undefined);
         },
 
         /**
@@ -39,9 +40,9 @@ function encodeSummary(output, summary) {
             @param {String} level
             @return {Object}
         */
-        getArticleByPath: function(level) {
-            var article = summary.getByPath(level);
-            return (article? encodeSummaryArticle(article) : undefined);
+        getArticleByPath(level) {
+            const article = summary.getByPath(level);
+            return (article ? encodeSummaryArticle(article) : undefined);
         }
     };
 
diff --git a/packages/gitbook/lib/api/index.js b/packages/gitbook/src/api/index.js
index 5e67525..5e67525 100644
--- a/packages/gitbook/lib/api/index.js
+++ b/packages/gitbook/src/api/index.js
diff --git a/packages/gitbook/lib/browser.js b/packages/gitbook/src/browser.js
index 87a4dc4..771ecd5 100644
--- a/packages/gitbook/lib/browser.js
+++ b/packages/gitbook/src/browser.js
@@ -1,4 +1,4 @@
-var Modifiers = require('./modifiers');
+const Modifiers = require('./modifiers');
 
 module.exports = {
     Parse:              require('./parse'),
diff --git a/packages/gitbook/lib/cli/build.js b/packages/gitbook/src/cli/build.js
index 023901e..3f5c937 100644
--- a/packages/gitbook/lib/cli/build.js
+++ b/packages/gitbook/src/cli/build.js
@@ -1,10 +1,10 @@
-var Parse = require('../parse');
-var Output = require('../output');
-var timing = require('../utils/timing');
+const Parse = require('../parse');
+const Output = require('../output');
+const timing = require('../utils/timing');
 
-var options = require('./options');
-var getBook = require('./getBook');
-var getOutputFolder = require('./getOutputFolder');
+const options = require('./options');
+const getBook = require('./getBook');
+const getOutputFolder = require('./getOutputFolder');
 
 
 module.exports = {
@@ -15,11 +15,11 @@ module.exports = {
         options.format,
         options.timing
     ],
-    exec: function(args, kwargs) {
-        var book = getBook(args, kwargs);
-        var outputFolder = getOutputFolder(args);
+    exec(args, kwargs) {
+        const book = getBook(args, kwargs);
+        const outputFolder = getOutputFolder(args);
 
-        var Generator = Output.getGenerator(kwargs.format);
+        const Generator = Output.getGenerator(kwargs.format);
 
         return Parse.parseBook(book)
         .then(function(resultBook) {
diff --git a/packages/gitbook/lib/cli/buildEbook.js b/packages/gitbook/src/cli/buildEbook.js
index a87fac7..56e63f8 100644
--- a/packages/gitbook/lib/cli/buildEbook.js
+++ b/packages/gitbook/src/cli/buildEbook.js
@@ -1,13 +1,13 @@
-var path = require('path');
-var tmp = require('tmp');
+const path = require('path');
+const tmp = require('tmp');
 
-var Promise = require('../utils/promise');
-var fs = require('../utils/fs');
-var Parse = require('../parse');
-var Output = require('../output');
+const Promise = require('../utils/promise');
+const fs = require('../utils/fs');
+const Parse = require('../parse');
+const Output = require('../output');
 
-var options = require('./options');
-var getBook = require('./getBook');
+const options = require('./options');
+const getBook = require('./getBook');
 
 
 module.exports = function(format) {
@@ -17,37 +17,37 @@ module.exports = function(format) {
         options: [
             options.log
         ],
-        exec: function(args, kwargs) {
-            var extension = '.' + format;
+        exec(args, kwargs) {
+            const extension = '.' + format;
 
             // Output file will be stored in
-            var outputFile = args[1] || ('book' + extension);
+            const outputFile = args[1] || ('book' + extension);
 
             // Create temporary directory
-            var outputFolder = tmp.dirSync().name;
+            const outputFolder = tmp.dirSync().name;
 
-            var book = getBook(args, kwargs);
-            var logger = book.getLogger();
-            var Generator = Output.getGenerator('ebook');
+            const book = getBook(args, kwargs);
+            const logger = book.getLogger();
+            const Generator = Output.getGenerator('ebook');
 
             return Parse.parseBook(book)
             .then(function(resultBook) {
                 return Output.generate(Generator, resultBook, {
                     root: outputFolder,
-                    format: format
+                    format
                 });
             })
 
             // Extract ebook file
             .then(function(output) {
-                var book = output.getBook();
-                var languages = book.getLanguages();
+                const book = output.getBook();
+                const languages = book.getLanguages();
 
                 if (book.isMultilingual()) {
                     return Promise.forEach(languages.getList(), function(lang) {
-                        var langID = lang.getID();
+                        const langID = lang.getID();
 
-                        var langOutputFile = path.join(
+                        const langOutputFile = path.join(
                             path.dirname(outputFile),
                             path.basename(outputFile, extension) + '_' + langID + extension
                         );
diff --git a/packages/gitbook/src/cli/getBook.js b/packages/gitbook/src/cli/getBook.js
new file mode 100644
index 0000000..b37e49c
--- /dev/null
+++ b/packages/gitbook/src/cli/getBook.js
@@ -0,0 +1,23 @@
+const path = require('path');
+const Book = require('../models/book');
+const createNodeFS = require('../fs/node');
+
+/**
+    Return a book instance to work on from
+    command line args/kwargs
+
+    @param {Array} args
+    @param {Object} kwargs
+    @return {Book}
+*/
+function getBook(args, kwargs) {
+    const input = path.resolve(args[0] || process.cwd());
+    const logLevel = kwargs.log;
+
+    const fs = createNodeFS(input);
+    const book = Book.createForFS(fs);
+
+    return book.setLogLevel(logLevel);
+}
+
+module.exports = getBook;
diff --git a/packages/gitbook/src/cli/getOutputFolder.js b/packages/gitbook/src/cli/getOutputFolder.js
new file mode 100644
index 0000000..94f22da
--- /dev/null
+++ b/packages/gitbook/src/cli/getOutputFolder.js
@@ -0,0 +1,17 @@
+const path = require('path');
+
+/**
+    Return path to output folder
+
+    @param {Array} args
+    @return {String}
+*/
+function getOutputFolder(args) {
+    const bookRoot = path.resolve(args[0] || process.cwd());
+    const defaultOutputRoot = path.join(bookRoot, '_book');
+    const outputFolder = args[1] ? path.resolve(process.cwd(), args[1]) : defaultOutputRoot;
+
+    return outputFolder;
+}
+
+module.exports = getOutputFolder;
diff --git a/packages/gitbook/lib/cli/index.js b/packages/gitbook/src/cli/index.js
index f1fca1d..48ad117 100644
--- a/packages/gitbook/lib/cli/index.js
+++ b/packages/gitbook/src/cli/index.js
@@ -1,4 +1,4 @@
-var buildEbook = require('./buildEbook');
+const buildEbook = require('./buildEbook');
 
 module.exports = [
     require('./build'),
diff --git a/packages/gitbook/src/cli/init.js b/packages/gitbook/src/cli/init.js
new file mode 100644
index 0000000..51d6869
--- /dev/null
+++ b/packages/gitbook/src/cli/init.js
@@ -0,0 +1,17 @@
+const path = require('path');
+
+const options = require('./options');
+const initBook = require('../init');
+
+module.exports = {
+    name: 'init [book]',
+    description: 'setup and create files for chapters',
+    options: [
+        options.log
+    ],
+    exec(args, kwargs) {
+        const bookRoot = path.resolve(process.cwd(), args[0] || './');
+
+        return initBook(bookRoot);
+    }
+};
diff --git a/packages/gitbook/lib/cli/install.js b/packages/gitbook/src/cli/install.js
index c001711..6af4013 100644
--- a/packages/gitbook/lib/cli/install.js
+++ b/packages/gitbook/src/cli/install.js
@@ -1,8 +1,8 @@
-var options = require('./options');
-var getBook = require('./getBook');
+const options = require('./options');
+const getBook = require('./getBook');
 
-var Parse = require('../parse');
-var Plugins = require('../plugins');
+const Parse = require('../parse');
+const Plugins = require('../plugins');
 
 module.exports = {
     name: 'install [book]',
@@ -10,8 +10,8 @@ module.exports = {
     options: [
         options.log
     ],
-    exec: function(args, kwargs) {
-        var book = getBook(args, kwargs);
+    exec(args, kwargs) {
+        const book = getBook(args, kwargs);
 
         return Parse.parseConfig(book)
         .then(function(resultBook) {
diff --git a/packages/gitbook/lib/cli/options.js b/packages/gitbook/src/cli/options.js
index 72961ab..d643f91 100644
--- a/packages/gitbook/lib/cli/options.js
+++ b/packages/gitbook/src/cli/options.js
@@ -1,6 +1,6 @@
-var Logger = require('../utils/logger');
+const Logger = require('../utils/logger');
 
-var logOptions = {
+const logOptions = {
     name: 'log',
     description: 'Minimum log level to display',
     values: Logger.LEVELS
@@ -11,14 +11,14 @@ var logOptions = {
     defaults: 'info'
 };
 
-var formatOption = {
+const formatOption = {
     name: 'format',
     description: 'Format to build to',
     values: ['website', 'json', 'ebook'],
     defaults: 'website'
 };
 
-var timingOption = {
+const timingOption = {
     name: 'timing',
     description: 'Print timing debug information',
     defaults: false
diff --git a/packages/gitbook/lib/cli/parse.js b/packages/gitbook/src/cli/parse.js
index 0fa509a..3d38fe7 100644
--- a/packages/gitbook/lib/cli/parse.js
+++ b/packages/gitbook/src/cli/parse.js
@@ -1,22 +1,22 @@
-var options = require('./options');
-var getBook = require('./getBook');
+const options = require('./options');
+const getBook = require('./getBook');
 
-var Parse = require('../parse');
+const Parse = require('../parse');
 
 function printBook(book) {
-    var logger = book.getLogger();
+    const logger = book.getLogger();
 
-    var config = book.getConfig();
-    var configFile = config.getFile();
+    const config = book.getConfig();
+    const configFile = config.getFile();
 
-    var summary = book.getSummary();
-    var summaryFile = summary.getFile();
+    const summary = book.getSummary();
+    const summaryFile = summary.getFile();
 
-    var readme = book.getReadme();
-    var readmeFile = readme.getFile();
+    const readme = book.getReadme();
+    const readmeFile = readme.getFile();
 
-    var glossary = book.getGlossary();
-    var glossaryFile = glossary.getFile();
+    const glossary = book.getGlossary();
+    const glossaryFile = glossary.getFile();
 
     if (configFile.exists()) {
         logger.info.ln('Configuration file is', configFile.getPath());
@@ -36,9 +36,9 @@ function printBook(book) {
 }
 
 function printMultingualBook(book) {
-    var logger = book.getLogger();
-    var languages = book.getLanguages();
-    var books = book.getBooks();
+    const logger = book.getLogger();
+    const languages = book.getLanguages();
+    const books = book.getBooks();
 
     logger.info.ln(languages.size + ' languages');
 
@@ -55,14 +55,14 @@ module.exports = {
     options: [
         options.log
     ],
-    exec: function(args, kwargs) {
-        var book = getBook(args, kwargs);
-        var logger = book.getLogger();
+    exec(args, kwargs) {
+        const book = getBook(args, kwargs);
+        const logger = book.getLogger();
 
         return Parse.parseBook(book)
         .then(function(resultBook) {
-            var rootFolder = book.getRoot();
-            var contentFolder = book.getContentRoot();
+            const rootFolder = book.getRoot();
+            const contentFolder = book.getContentRoot();
 
             logger.info.ln('Book located in:', rootFolder);
             if (contentFolder != rootFolder) {
diff --git a/packages/gitbook/lib/cli/serve.js b/packages/gitbook/src/cli/serve.js
index 5340851..6397c2e 100644
--- a/packages/gitbook/lib/cli/serve.js
+++ b/packages/gitbook/src/cli/serve.js
@@ -1,24 +1,24 @@
 /* eslint-disable no-console */
 
-var tinylr = require('tiny-lr');
-var open = require('open');
+const tinylr = require('tiny-lr');
+const open = require('open');
 
-var Parse = require('../parse');
-var Output = require('../output');
-var ConfigModifier = require('../modifiers').Config;
+const Parse = require('../parse');
+const Output = require('../output');
+const ConfigModifier = require('../modifiers').Config;
 
-var Promise = require('../utils/promise');
+const Promise = require('../utils/promise');
 
-var options = require('./options');
-var getBook = require('./getBook');
-var getOutputFolder = require('./getOutputFolder');
-var Server = require('./server');
-var watch = require('./watch');
+const options = require('./options');
+const getBook = require('./getBook');
+const getOutputFolder = require('./getOutputFolder');
+const Server = require('./server');
+const watch = require('./watch');
 
-var server, lrServer, lrPath;
+let server, lrServer, lrPath;
 
 function waitForCtrlC() {
-    var d = Promise.defer();
+    const d = Promise.defer();
 
     process.on('SIGINT', function() {
         d.resolve();
@@ -29,15 +29,15 @@ function waitForCtrlC() {
 
 
 function generateBook(args, kwargs) {
-    var port = kwargs.port;
-    var outputFolder = getOutputFolder(args);
-    var book = getBook(args, kwargs);
-    var Generator = Output.getGenerator(kwargs.format);
-    var browser = kwargs['browser'];
+    const port = kwargs.port;
+    const outputFolder = getOutputFolder(args);
+    const book = getBook(args, kwargs);
+    const Generator = Output.getGenerator(kwargs.format);
+    const browser = kwargs['browser'];
 
-    var hasWatch = kwargs['watch'];
-    var hasLiveReloading = kwargs['live'];
-    var hasOpen = kwargs['open'];
+    const hasWatch = kwargs['watch'];
+    const hasLiveReloading = kwargs['live'];
+    const hasOpen = kwargs['open'];
 
     // Stop server if running
     if (server.isRunning()) console.log('Stopping server');
@@ -48,7 +48,7 @@ function generateBook(args, kwargs) {
         .then(function(resultBook) {
             if (hasLiveReloading) {
                 // Enable livereload plugin
-                var config = resultBook.getConfig();
+                let config = resultBook.getConfig();
                 config = ConfigModifier.addPlugin(config, 'livereload');
                 resultBook = resultBook.set('config', config);
             }
@@ -64,7 +64,7 @@ function generateBook(args, kwargs) {
         return server.start(outputFolder, port);
     })
     .then(function() {
-        console.log('Serving book on http://localhost:'+port);
+        console.log('Serving book on http://localhost:' + port);
 
         if (lrPath && hasLiveReloading) {
             // trigger livereload
@@ -76,7 +76,7 @@ function generateBook(args, kwargs) {
         }
 
         if (hasOpen) {
-            open('http://localhost:'+port, browser);
+            open('http://localhost:' + port, browser);
         }
     })
     .then(function() {
@@ -132,10 +132,10 @@ module.exports = {
         options.log,
         options.format
     ],
-    exec: function(args, kwargs) {
+    exec(args, kwargs) {
         server = new Server();
-        var hasWatch = kwargs['watch'];
-        var hasLiveReloading = kwargs['live'];
+        const hasWatch = kwargs['watch'];
+        const hasLiveReloading = kwargs['live'];
 
         return Promise()
         .then(function() {
diff --git a/packages/gitbook/src/cli/server.js b/packages/gitbook/src/cli/server.js
new file mode 100644
index 0000000..c494efc
--- /dev/null
+++ b/packages/gitbook/src/cli/server.js
@@ -0,0 +1,127 @@
+const events = require('events');
+const http = require('http');
+const send = require('send');
+const url = require('url');
+
+const Promise = require('../utils/promise');
+
+class Server extends events.EventEmitter {
+    constructor() {
+        super();
+        this.running = null;
+        this.dir = null;
+        this.port = 0;
+        this.sockets = [];
+    }
+
+    /**
+     * Return true if the server is running
+     * @return {Boolean}
+     */
+    isRunning() {
+        return !!this.running;
+    }
+
+    /**
+     * Stop the server
+     * @return {Promise}
+     */
+    stop() {
+        const that = this;
+        if (!this.isRunning()) return Promise();
+
+        const d = Promise.defer();
+        this.running.close(function(err) {
+            that.running = null;
+            that.emit('state', false);
+
+            if (err) d.reject(err);
+            else d.resolve();
+        });
+
+        for (let i = 0; i < this.sockets.length; i++) {
+            this.sockets[i].destroy();
+        }
+
+        return d.promise;
+    }
+
+    /**
+     * Start the server
+     * @return {Promise}
+     */
+    start(dir, port) {
+        const that = this;
+        let pre = Promise();
+        port = port || 8004;
+
+        if (that.isRunning()) pre = this.stop();
+        return pre
+        .then(function() {
+            const d = Promise.defer();
+
+            that.running = http.createServer(function(req, res) {
+                // Render error
+                function error(err) {
+                    res.statusCode = err.status || 500;
+                    res.end(err.message);
+                }
+
+                // Redirect to directory's index.html
+                function redirect() {
+                    const resultURL = urlTransform(req.url, function(parsed) {
+                        parsed.pathname += '/';
+                        return parsed;
+                    });
+
+                    res.statusCode = 301;
+                    res.setHeader('Location', resultURL);
+                    res.end('Redirecting to ' + resultURL);
+                }
+
+                res.setHeader('X-Current-Location', req.url);
+
+                // Send file
+                send(req, url.parse(req.url).pathname, {
+                    root: dir
+                })
+                .on('error', error)
+                .on('directory', redirect)
+                .pipe(res);
+            });
+
+            that.running.on('connection', function(socket) {
+                that.sockets.push(socket);
+                socket.setTimeout(4000);
+                socket.on('close', function() {
+                    that.sockets.splice(that.sockets.indexOf(socket), 1);
+                });
+            });
+
+            that.running.listen(port, function(err) {
+                if (err) return d.reject(err);
+
+                that.port = port;
+                that.dir = dir;
+                that.emit('state', true);
+                d.resolve();
+            });
+
+            return d.promise;
+        });
+    }
+}
+
+/**
+ * urlTransform is a helper function that allows a function to transform
+ * a url string in it's parsed form and returns the new url as a string
+ *
+ * @param {String} uri
+ * @param {Function} fn
+ * @return {String}
+ */
+function urlTransform(uri, fn) {
+    return url.format(fn(url.parse(uri)));
+}
+
+module.exports = Server;
diff --git a/packages/gitbook/lib/cli/watch.js b/packages/gitbook/src/cli/watch.js
index 14434ab..e1d453c 100644
--- a/packages/gitbook/lib/cli/watch.js
+++ b/packages/gitbook/src/cli/watch.js
@@ -1,8 +1,8 @@
-var path = require('path');
-var chokidar = require('chokidar');
+const path = require('path');
+const chokidar = require('chokidar');
 
-var Promise = require('../utils/promise');
-var parsers = require('../parsers');
+const Promise = require('../utils/promise');
+const parsers = require('../parsers');
 
 /**
     Watch a folder and resolve promise once a file is modified
@@ -11,19 +11,19 @@ var parsers = require('../parsers');
     @return {Promise}
 */
 function watch(dir) {
-    var d = Promise.defer();
+    const d = Promise.defer();
     dir = path.resolve(dir);
 
-    var toWatch = [
+    const toWatch = [
         'book.json', 'book.js', '_layouts/**'
     ];
 
     // Watch all parsable files
     parsers.extensions.forEach(function(ext) {
-        toWatch.push('**/*'+ext);
+        toWatch.push('**/*' + ext);
     });
 
-    var watcher = chokidar.watch(toWatch, {
+    const watcher = chokidar.watch(toWatch, {
         cwd: dir,
         ignored: '_book/**',
         ignoreInitial: true
diff --git a/packages/gitbook/lib/constants/__tests__/configSchema.js b/packages/gitbook/src/constants/__tests__/configSchema.js
index efc99b9..df83680 100644
--- a/packages/gitbook/lib/constants/__tests__/configSchema.js
+++ b/packages/gitbook/src/constants/__tests__/configSchema.js
@@ -1,10 +1,10 @@
-var jsonschema = require('jsonschema');
-var schema = require('../configSchema');
+const jsonschema = require('jsonschema');
+const schema = require('../configSchema');
 
 describe('configSchema', function() {
 
     function validate(cfg) {
-        var v = new jsonschema.Validator();
+        const v = new jsonschema.Validator();
         return v.validate(cfg, schema, {
             propertyName: 'config'
         });
@@ -13,7 +13,7 @@ describe('configSchema', function() {
     describe('structure', function() {
 
         it('should accept dot in filename', function() {
-            var result = validate({
+            const result = validate({
                 structure: {
                     readme: 'book-intro.adoc'
                 }
@@ -23,7 +23,7 @@ describe('configSchema', function() {
         });
 
         it('should accept uppercase in filename', function() {
-            var result = validate({
+            const result = validate({
                 structure: {
                     readme: 'BOOK.adoc'
                 }
@@ -33,7 +33,7 @@ describe('configSchema', function() {
         });
 
         it('should not accept filepath', function() {
-            var result = validate({
+            const result = validate({
                 structure: {
                     readme: 'folder/myFile.md'
                 }
diff --git a/packages/gitbook/src/constants/configDefault.js b/packages/gitbook/src/constants/configDefault.js
new file mode 100644
index 0000000..c384c6c
--- /dev/null
+++ b/packages/gitbook/src/constants/configDefault.js
@@ -0,0 +1,6 @@
+const Immutable = require('immutable');
+const jsonSchemaDefaults = require('json-schema-defaults');
+
+const schema = require('./configSchema');
+
+module.exports = Immutable.fromJS(jsonSchemaDefaults(schema));
diff --git a/packages/gitbook/lib/constants/configFiles.js b/packages/gitbook/src/constants/configFiles.js
index a67fd74..a67fd74 100644
--- a/packages/gitbook/lib/constants/configFiles.js
+++ b/packages/gitbook/src/constants/configFiles.js
diff --git a/packages/gitbook/lib/constants/configSchema.js b/packages/gitbook/src/constants/configSchema.js
index d2126c6..9aaf8cd 100644
--- a/packages/gitbook/lib/constants/configSchema.js
+++ b/packages/gitbook/src/constants/configSchema.js
@@ -1,4 +1,4 @@
-var FILENAME_REGEX = '^[a-zA-Z-._\d,\s]+$';
+const FILENAME_REGEX = '^[a-zA-Z-._\d,\s]+$';
 
 module.exports = {
     '$schema': 'http://json-schema.org/schema#',
diff --git a/packages/gitbook/lib/constants/defaultBlocks.js b/packages/gitbook/src/constants/defaultBlocks.js
index 74d1f1f..05c9b09 100644
--- a/packages/gitbook/lib/constants/defaultBlocks.js
+++ b/packages/gitbook/src/constants/defaultBlocks.js
@@ -1,17 +1,17 @@
-var Immutable = require('immutable');
-var TemplateBlock = require('../models/templateBlock');
+const Immutable = require('immutable');
+const TemplateBlock = require('../models/templateBlock');
 
 module.exports = Immutable.Map({
     html: TemplateBlock({
         name: 'html',
-        process: function(blk) {
+        process(blk) {
             return blk;
         }
     }),
 
     code: TemplateBlock({
         name: 'code',
-        process: function(blk) {
+        process(blk) {
             return {
                 html: false,
                 body: blk.body
@@ -21,7 +21,7 @@ module.exports = Immutable.Map({
 
     markdown: TemplateBlock({
         name: 'markdown',
-        process: function(blk) {
+        process(blk) {
             return this.book.renderInline('markdown', blk.body)
             .then(function(out) {
                 return { body: out };
@@ -31,7 +31,7 @@ module.exports = Immutable.Map({
 
     asciidoc: TemplateBlock({
         name: 'asciidoc',
-        process: function(blk) {
+        process(blk) {
             return this.book.renderInline('asciidoc', blk.body)
             .then(function(out) {
                 return { body: out };
@@ -41,7 +41,7 @@ module.exports = Immutable.Map({
 
     markup: TemplateBlock({
         name: 'markup',
-        process: function(blk) {
+        process(blk) {
             return this.book.renderInline(this.ctx.file.type, blk.body)
             .then(function(out) {
                 return { body: out };
diff --git a/packages/gitbook/lib/constants/defaultFilters.js b/packages/gitbook/src/constants/defaultFilters.js
index 35025cc..c9bffe1 100644
--- a/packages/gitbook/lib/constants/defaultFilters.js
+++ b/packages/gitbook/src/constants/defaultFilters.js
@@ -1,15 +1,15 @@
-var Immutable = require('immutable');
-var moment = require('moment');
+const Immutable = require('immutable');
+const moment = require('moment');
 
 module.exports = Immutable.Map({
     // Format a date
     // ex: 'MMMM Do YYYY, h:mm:ss a
-    date: function(time, format) {
+    date(time, format) {
         return moment(time).format(format);
     },
 
     // Relative Time
-    dateFromNow: function(time) {
+    dateFromNow(time) {
         return moment(time).fromNow();
     }
 });
diff --git a/packages/gitbook/lib/constants/defaultPlugins.js b/packages/gitbook/src/constants/defaultPlugins.js
index 6d15971..cd1c0c8 100644
--- a/packages/gitbook/lib/constants/defaultPlugins.js
+++ b/packages/gitbook/src/constants/defaultPlugins.js
@@ -1,7 +1,7 @@
-var Immutable = require('immutable');
-var PluginDependency = require('../models/pluginDependency');
+const Immutable = require('immutable');
+const PluginDependency = require('../models/pluginDependency');
 
-var pkg = require('../../package.json');
+const pkg = require('../../package.json');
 
 /**
  * Create a PluginDependency from a dependency of gitbook
@@ -9,8 +9,8 @@ var pkg = require('../../package.json');
  * @return {PluginDependency}
  */
 function createFromDependency(pluginName) {
-    var npmID = PluginDependency.nameToNpmID(pluginName);
-    var version = pkg.dependencies[npmID];
+    const npmID = PluginDependency.nameToNpmID(pluginName);
+    const version = pkg.dependencies[npmID];
 
     return PluginDependency.create(pluginName, version);
 }
diff --git a/packages/gitbook/lib/constants/extsAsciidoc.js b/packages/gitbook/src/constants/extsAsciidoc.js
index b2f4ce4..b2f4ce4 100644
--- a/packages/gitbook/lib/constants/extsAsciidoc.js
+++ b/packages/gitbook/src/constants/extsAsciidoc.js
diff --git a/packages/gitbook/lib/constants/extsMarkdown.js b/packages/gitbook/src/constants/extsMarkdown.js
index 44bf36b..44bf36b 100644
--- a/packages/gitbook/lib/constants/extsMarkdown.js
+++ b/packages/gitbook/src/constants/extsMarkdown.js
diff --git a/packages/gitbook/lib/constants/ignoreFiles.js b/packages/gitbook/src/constants/ignoreFiles.js
index aac225e..aac225e 100644
--- a/packages/gitbook/lib/constants/ignoreFiles.js
+++ b/packages/gitbook/src/constants/ignoreFiles.js
diff --git a/packages/gitbook/lib/constants/pluginAssetsFolder.js b/packages/gitbook/src/constants/pluginAssetsFolder.js
index cd44722..cd44722 100644
--- a/packages/gitbook/lib/constants/pluginAssetsFolder.js
+++ b/packages/gitbook/src/constants/pluginAssetsFolder.js
diff --git a/packages/gitbook/lib/constants/pluginHooks.js b/packages/gitbook/src/constants/pluginHooks.js
index 2d5dcaa..2d5dcaa 100644
--- a/packages/gitbook/lib/constants/pluginHooks.js
+++ b/packages/gitbook/src/constants/pluginHooks.js
diff --git a/packages/gitbook/lib/constants/pluginPrefix.js b/packages/gitbook/src/constants/pluginPrefix.js
index c7f2dd0..c7f2dd0 100644
--- a/packages/gitbook/lib/constants/pluginPrefix.js
+++ b/packages/gitbook/src/constants/pluginPrefix.js
diff --git a/packages/gitbook/lib/constants/pluginResources.js b/packages/gitbook/src/constants/pluginResources.js
index ae283bf..cc9d134 100644
--- a/packages/gitbook/lib/constants/pluginResources.js
+++ b/packages/gitbook/src/constants/pluginResources.js
@@ -1,4 +1,4 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
 module.exports = Immutable.List([
     'js',
diff --git a/packages/gitbook/lib/constants/templatesFolder.js b/packages/gitbook/src/constants/templatesFolder.js
index aad6a72..aad6a72 100644
--- a/packages/gitbook/lib/constants/templatesFolder.js
+++ b/packages/gitbook/src/constants/templatesFolder.js
diff --git a/packages/gitbook/lib/constants/themePrefix.js b/packages/gitbook/src/constants/themePrefix.js
index 99428de..621e85c 100644
--- a/packages/gitbook/lib/constants/themePrefix.js
+++ b/packages/gitbook/src/constants/themePrefix.js
@@ -1,4 +1,4 @@
 /*
     All GitBook themes plugins name start with this prefix once shorted.
 */
-module.exports = 'theme-';
\ No newline at end of file
+module.exports = 'theme-';
diff --git a/packages/gitbook/lib/fs/__tests__/mock.js b/packages/gitbook/src/fs/__tests__/mock.js
index 04bd46a..7d1ea48 100644
--- a/packages/gitbook/lib/fs/__tests__/mock.js
+++ b/packages/gitbook/src/fs/__tests__/mock.js
@@ -1,7 +1,7 @@
-var createMockFS = require('../mock');
+const createMockFS = require('../mock');
 
 describe('MockFS', function() {
-    var fs = createMockFS({
+    const fs = createMockFS({
         'README.md': 'Hello World',
         'SUMMARY.md': '# Summary',
         'folder': {
@@ -79,4 +79,3 @@ describe('MockFS', function() {
     });
 });
 
-
diff --git a/packages/gitbook/lib/fs/mock.js b/packages/gitbook/src/fs/mock.js
index 784c533..91f3bd6 100644
--- a/packages/gitbook/lib/fs/mock.js
+++ b/packages/gitbook/src/fs/mock.js
@@ -1,10 +1,10 @@
-var path = require('path');
-var is = require('is');
-var Buffer = require('buffer').Buffer;
-var Immutable = require('immutable');
+const path = require('path');
+const is = require('is');
+const Buffer = require('buffer').Buffer;
+const Immutable = require('immutable');
 
-var FS = require('../models/fs');
-var error = require('../utils/error');
+const FS = require('../models/fs');
+const error = require('../utils/error');
 
 /**
     Create a fake filesystem for unit testing GitBook.
@@ -13,14 +13,14 @@ var error = require('../utils/error');
 */
 function createMockFS(files) {
     files = Immutable.fromJS(files);
-    var mtime = new Date();
+    const mtime = new Date();
 
     function getFile(filePath) {
-        var parts = path.normalize(filePath).split(path.sep);
+        const parts = path.normalize(filePath).split(path.sep);
         return parts.reduce(function(list, part, i) {
             if (!list) return null;
 
-            var file;
+            let file;
 
             if (!part || part === '.') file = list;
             else file = list.get(part);
@@ -41,7 +41,7 @@ function createMockFS(files) {
     }
 
     function fsReadFile(filePath) {
-        var file = getFile(filePath);
+        const file = getFile(filePath);
         if (!is.string(file)) {
             throw error.FileNotFoundError({
                 filename: filePath
@@ -52,7 +52,7 @@ function createMockFS(files) {
     }
 
     function fsStatFile(filePath) {
-        var file = getFile(filePath);
+        const file = getFile(filePath);
         if (!file) {
             throw error.FileNotFoundError({
                 filename: filePath
@@ -60,12 +60,12 @@ function createMockFS(files) {
         }
 
         return {
-            mtime: mtime
+            mtime
         };
     }
 
     function fsReadDir(filePath) {
-        var dir = getFile(filePath);
+        const dir = getFile(filePath);
         if (!dir || is.string(dir)) {
             throw error.FileNotFoundError({
                 filename: filePath
@@ -85,10 +85,10 @@ function createMockFS(files) {
 
     return FS.create({
         root: '',
-        fsExists: fsExists,
-        fsReadFile: fsReadFile,
-        fsStatFile: fsStatFile,
-        fsReadDir: fsReadDir
+        fsExists,
+        fsReadFile,
+        fsStatFile,
+        fsReadDir
     });
 }
 
diff --git a/packages/gitbook/lib/fs/node.js b/packages/gitbook/src/fs/node.js
index dfe9fae..6e28daf 100644
--- a/packages/gitbook/lib/fs/node.js
+++ b/packages/gitbook/src/fs/node.js
@@ -1,9 +1,9 @@
-var path = require('path');
-var Immutable = require('immutable');
-var fresh = require('fresh-require');
+const path = require('path');
+const Immutable = require('immutable');
+const fresh = require('fresh-require');
 
-var fs = require('../utils/fs');
-var FS = require('../models/fs');
+const fs = require('../utils/fs');
+const FS = require('../models/fs');
 
 function fsReadDir(folder) {
     return fs.readdir(folder)
@@ -14,7 +14,7 @@ function fsReadDir(folder) {
             .map(function(file) {
                 if (file == '.' || file == '..') return;
 
-                var stat = fs.statSync(path.join(folder, file));
+                const stat = fs.statSync(path.join(folder, file));
                 if (stat.isDirectory()) file = file + path.sep;
                 return file;
             })
@@ -30,13 +30,13 @@ function fsLoadObject(filename) {
 
 module.exports = function createNodeFS(root) {
     return FS.create({
-        root: root,
+        root,
 
         fsExists: fs.exists,
         fsReadFile: fs.readFile,
         fsStatFile: fs.stat,
-        fsReadDir: fsReadDir,
-        fsLoadObject: fsLoadObject,
+        fsReadDir,
+        fsLoadObject,
         fsReadAsStream: fs.readStream
     });
 };
diff --git a/packages/gitbook/lib/gitbook.js b/packages/gitbook/src/gitbook.js
index bafd3b8..5786e68 100644
--- a/packages/gitbook/lib/gitbook.js
+++ b/packages/gitbook/src/gitbook.js
@@ -1,10 +1,10 @@
-var semver = require('semver');
-var pkg = require('../package.json');
+const semver = require('semver');
+const pkg = require('../package.json');
 
-var VERSION = pkg.version;
-var VERSION_STABLE = VERSION.replace(/\-(\S+)/g, '');
+const VERSION = pkg.version;
+const VERSION_STABLE = VERSION.replace(/\-(\S+)/g, '');
 
-var START_TIME = new Date();
+const START_TIME = new Date();
 
 /**
     Verify that this gitbook version satisfies a requirement
@@ -23,6 +23,6 @@ function satisfies(condition) {
 
 module.exports = {
     version: pkg.version,
-    satisfies: satisfies,
-    START_TIME: START_TIME
+    satisfies,
+    START_TIME
 };
diff --git a/packages/gitbook/lib/index.js b/packages/gitbook/src/index.js
index 1f683e2..7919000 100644
--- a/packages/gitbook/lib/index.js
+++ b/packages/gitbook/src/index.js
@@ -1,6 +1,6 @@
-var extend = require('extend');
+const extend = require('extend');
 
-var common = require('./browser');
+const common = require('./browser');
 
 module.exports = extend({
     initBook:       require('./init'),
diff --git a/packages/gitbook/lib/init.js b/packages/gitbook/src/init.js
index c112d4d..bbd5f90 100644
--- a/packages/gitbook/lib/init.js
+++ b/packages/gitbook/src/init.js
@@ -1,12 +1,12 @@
-var path = require('path');
+const path = require('path');
 
-var createNodeFS = require('./fs/node');
-var fs = require('./utils/fs');
-var Promise = require('./utils/promise');
-var File = require('./models/file');
-var Readme = require('./models/readme');
-var Book = require('./models/book');
-var Parse = require('./parse');
+const createNodeFS = require('./fs/node');
+const fs = require('./utils/fs');
+const Promise = require('./utils/promise');
+const File = require('./models/file');
+const Readme = require('./models/readme');
+const Book = require('./models/book');
+const Parse = require('./parse');
 
 /**
     Initialize folder structure for a book
@@ -17,38 +17,38 @@ var Parse = require('./parse');
     @return {Promise}
 */
 function initBook(rootFolder) {
-    var extension = '.md';
+    const extension = '.md';
 
     return fs.mkdirp(rootFolder)
 
     // Parse the summary and readme
     .then(function() {
-        var fs = createNodeFS(rootFolder);
-        var book = Book.createForFS(fs);
+        const bookFS = createNodeFS(rootFolder);
+        const book = Book.createForFS(bookFS);
 
         return Parse.parseReadme(book)
 
         // Setup default readme if doesn't found one
         .fail(function() {
-            var readmeFile = File.createWithFilepath('README' + extension);
-            var readme = Readme.create(readmeFile);
+            const readmeFile = File.createWithFilepath('README' + extension);
+            const readme = Readme.create(readmeFile);
             return book.setReadme(readme);
         });
     })
     .then(Parse.parseSummary)
 
     .then(function(book) {
-        var logger = book.getLogger();
-        var summary = book.getSummary();
-        var summaryFile = summary.getFile();
-        var summaryFilename = summaryFile.getPath() || ('SUMMARY' + extension);
+        const logger = book.getLogger();
+        const summary = book.getSummary();
+        const summaryFile = summary.getFile();
+        const summaryFilename = summaryFile.getPath() || ('SUMMARY' + extension);
 
-        var articles = summary.getArticlesAsList();
+        const articles = summary.getArticlesAsList();
 
         // Write pages
         return Promise.forEach(articles, function(article) {
-            var articlePath = article.getPath();
-            var filePath = articlePath? path.join(rootFolder, articlePath) : null;
+            const articlePath = article.getPath();
+            const filePath = articlePath ? path.join(rootFolder, articlePath) : null;
             if (!filePath) {
                 return;
             }
@@ -64,7 +64,7 @@ function initBook(rootFolder) {
 
         // Write summary
         .then(function() {
-            var filePath = path.join(rootFolder, summaryFilename);
+            const filePath = path.join(rootFolder, summaryFilename);
 
             return fs.ensureFile(filePath)
             .then(function() {
diff --git a/packages/gitbook/src/json/encodeBook.js b/packages/gitbook/src/json/encodeBook.js
new file mode 100644
index 0000000..0b259a9
--- /dev/null
+++ b/packages/gitbook/src/json/encodeBook.js
@@ -0,0 +1,39 @@
+const extend = require('extend');
+
+const gitbook = require('../gitbook');
+const encodeSummary = require('./encodeSummary');
+const encodeGlossary = require('./encodeGlossary');
+const encodeReadme = require('./encodeReadme');
+const encodeLanguages = require('./encodeLanguages');
+
+/**
+    Encode a book to JSON
+
+    @param {Book}
+    @return {Object}
+*/
+function encodeBookToJson(book) {
+    const config = book.getConfig();
+    const language = book.getLanguage();
+
+    const variables = config.getValue('variables', {});
+
+    return {
+        summary: encodeSummary(book.getSummary()),
+        glossary: encodeGlossary(book.getGlossary()),
+        readme: encodeReadme(book.getReadme()),
+        config: book.getConfig().getValues().toJS(),
+
+        languages: book.isMultilingual() ? encodeLanguages(book.getLanguages()) : undefined,
+
+        gitbook: {
+            version: gitbook.version,
+            time: gitbook.START_TIME
+        },
+        book: extend({
+            language: language ? language : undefined
+        }, variables.toJS())
+    };
+}
+
+module.exports = encodeBookToJson;
diff --git a/packages/gitbook/lib/json/encodeBookWithPage.js b/packages/gitbook/src/json/encodeBookWithPage.js
index 1c5c7a3..f593af2 100644
--- a/packages/gitbook/lib/json/encodeBookWithPage.js
+++ b/packages/gitbook/src/json/encodeBookWithPage.js
@@ -1,6 +1,6 @@
-var encodeBook = require('./encodeBook');
-var encodePage = require('./encodePage');
-var encodeFile = require('./encodeFile');
+const encodeBook = require('./encodeBook');
+const encodePage = require('./encodePage');
+const encodeFile = require('./encodeFile');
 
 /**
  * Return a JSON representation of a book with a specific file
@@ -10,9 +10,9 @@ var encodeFile = require('./encodeFile');
  * @return {Object}
  */
 function encodeBookWithPage(book, page) {
-    var file = page.getFile();
+    const file = page.getFile();
 
-    var result = encodeBook(book);
+    const result = encodeBook(book);
     result.page = encodePage(page, book.getSummary());
     result.file = encodeFile(file);
 
diff --git a/packages/gitbook/lib/json/encodeFile.js b/packages/gitbook/src/json/encodeFile.js
index d2c9e8a..487a74c 100644
--- a/packages/gitbook/lib/json/encodeFile.js
+++ b/packages/gitbook/src/json/encodeFile.js
@@ -6,7 +6,7 @@
     @return {Object}
 */
 function encodeFileToJson(file) {
-    var filePath = file.getPath();
+    const filePath = file.getPath();
     if (!filePath) {
         return undefined;
     }
diff --git a/packages/gitbook/lib/json/encodeGlossary.js b/packages/gitbook/src/json/encodeGlossary.js
index e9bcfc9..6bdd683 100644
--- a/packages/gitbook/lib/json/encodeGlossary.js
+++ b/packages/gitbook/src/json/encodeGlossary.js
@@ -1,5 +1,5 @@
-var encodeFile = require('./encodeFile');
-var encodeGlossaryEntry = require('./encodeGlossaryEntry');
+const encodeFile = require('./encodeFile');
+const encodeGlossaryEntry = require('./encodeGlossaryEntry');
 
 /**
     Encode a glossary to JSON
@@ -8,8 +8,8 @@ var encodeGlossaryEntry = require('./encodeGlossaryEntry');
     @return {Object}
 */
 function encodeGlossary(glossary) {
-    var file = glossary.getFile();
-    var entries = glossary.getEntries();
+    const file = glossary.getFile();
+    const entries = glossary.getEntries();
 
     return {
         file: encodeFile(file),
diff --git a/packages/gitbook/lib/json/encodeGlossaryEntry.js b/packages/gitbook/src/json/encodeGlossaryEntry.js
index d163f45..d163f45 100644
--- a/packages/gitbook/lib/json/encodeGlossaryEntry.js
+++ b/packages/gitbook/src/json/encodeGlossaryEntry.js
diff --git a/packages/gitbook/lib/json/encodeLanguages.js b/packages/gitbook/src/json/encodeLanguages.js
index 8447e80..fc7487b 100644
--- a/packages/gitbook/lib/json/encodeLanguages.js
+++ b/packages/gitbook/src/json/encodeLanguages.js
@@ -1,4 +1,4 @@
-var encodeFile = require('./encodeFile');
+const encodeFile = require('./encodeFile');
 
 /**
     Encode a languages listing to JSON
@@ -7,8 +7,8 @@ var encodeFile = require('./encodeFile');
     @return {Object}
 */
 function encodeLanguages(languages) {
-    var file = languages.getFile();
-    var list = languages.getList();
+    const file = languages.getFile();
+    const list = languages.getList();
 
     return {
         file: encodeFile(file),
diff --git a/packages/gitbook/lib/json/encodeOutput.js b/packages/gitbook/src/json/encodeOutput.js
index 7347e57..31e5757 100644
--- a/packages/gitbook/lib/json/encodeOutput.js
+++ b/packages/gitbook/src/json/encodeOutput.js
@@ -1,4 +1,4 @@
-var encodeBook = require('./encodeBook');
+const encodeBook = require('./encodeBook');
 
 /**
  * Encode an output to JSON
@@ -7,11 +7,11 @@ var encodeBook = require('./encodeBook');
  * @return {Object}
  */
 function encodeOutputToJson(output) {
-    var book = output.getBook();
-    var generator = output.getGenerator();
-    var options = output.getOptions();
+    const book = output.getBook();
+    const generator = output.getGenerator();
+    const options = output.getOptions();
 
-    var result = encodeBook(book);
+    const result = encodeBook(book);
 
     result.output = {
         name: generator
diff --git a/packages/gitbook/lib/json/encodeOutputWithPage.js b/packages/gitbook/src/json/encodeOutputWithPage.js
index 8b21e3d..58db070 100644
--- a/packages/gitbook/lib/json/encodeOutputWithPage.js
+++ b/packages/gitbook/src/json/encodeOutputWithPage.js
@@ -1,6 +1,6 @@
-var encodeOutput = require('./encodeOutput');
-var encodePage = require('./encodePage');
-var encodeFile = require('./encodeFile');
+const encodeOutput = require('./encodeOutput');
+const encodePage = require('./encodePage');
+const encodeFile = require('./encodeFile');
 
 /**
  * Return a JSON representation of a book with a specific file
@@ -10,10 +10,10 @@ var encodeFile = require('./encodeFile');
  * @return {Object}
  */
 function encodeOutputWithPage(output, page) {
-    var file = page.getFile();
-    var book = output.getBook();
+    const file = page.getFile();
+    const book = output.getBook();
 
-    var result = encodeOutput(output);
+    const result = encodeOutput(output);
     result.page = encodePage(page, book.getSummary());
     result.file = encodeFile(file);
 
diff --git a/packages/gitbook/lib/json/encodePage.js b/packages/gitbook/src/json/encodePage.js
index be92117..b20a40c 100644
--- a/packages/gitbook/lib/json/encodePage.js
+++ b/packages/gitbook/src/json/encodePage.js
@@ -1,4 +1,4 @@
-var encodeSummaryArticle = require('./encodeSummaryArticle');
+const encodeSummaryArticle = require('./encodeSummaryArticle');
 
 /**
     Return a JSON representation of a page
@@ -8,23 +8,23 @@ var encodeSummaryArticle = require('./encodeSummaryArticle');
     @return {Object}
 */
 function encodePage(page, summary) {
-    var file = page.getFile();
-    var attributes = page.getAttributes();
-    var article = summary.getByPath(file.getPath());
+    const file = page.getFile();
+    const attributes = page.getAttributes();
+    const article = summary.getByPath(file.getPath());
 
-    var result = attributes.toJS();
+    const result = attributes.toJS();
 
     if (article) {
         result.title = article.getTitle();
         result.level = article.getLevel();
         result.depth = article.getDepth();
 
-        var nextArticle = summary.getNextArticle(article);
+        const nextArticle = summary.getNextArticle(article);
         if (nextArticle) {
             result.next = encodeSummaryArticle(nextArticle);
         }
 
-        var prevArticle = summary.getPrevArticle(article);
+        const prevArticle = summary.getPrevArticle(article);
         if (prevArticle) {
             result.previous = encodeSummaryArticle(prevArticle);
         }
diff --git a/packages/gitbook/lib/json/encodeReadme.js b/packages/gitbook/src/json/encodeReadme.js
index 96176a3..cc71bcb 100644
--- a/packages/gitbook/lib/json/encodeReadme.js
+++ b/packages/gitbook/src/json/encodeReadme.js
@@ -1,4 +1,4 @@
-var encodeFile = require('./encodeFile');
+const encodeFile = require('./encodeFile');
 
 /**
     Encode a readme to JSON
@@ -7,7 +7,7 @@ var encodeFile = require('./encodeFile');
     @return {Object}
 */
 function encodeReadme(readme) {
-    var file = readme.getFile();
+    const file = readme.getFile();
 
     return {
         file: encodeFile(file)
diff --git a/packages/gitbook/lib/json/encodeSummary.js b/packages/gitbook/src/json/encodeSummary.js
index 97db910..9a07da4 100644
--- a/packages/gitbook/lib/json/encodeSummary.js
+++ b/packages/gitbook/src/json/encodeSummary.js
@@ -1,5 +1,5 @@
-var encodeFile = require('./encodeFile');
-var encodeSummaryPart = require('./encodeSummaryPart');
+const encodeFile = require('./encodeFile');
+const encodeSummaryPart = require('./encodeSummaryPart');
 
 /**
     Encode a summary to JSON
@@ -8,8 +8,8 @@ var encodeSummaryPart = require('./encodeSummaryPart');
     @return {Object}
 */
 function encodeSummary(summary) {
-    var file = summary.getFile();
-    var parts = summary.getParts();
+    const file = summary.getFile();
+    const parts = summary.getParts();
 
     return {
         file: encodeFile(file),
diff --git a/packages/gitbook/lib/json/encodeSummaryArticle.js b/packages/gitbook/src/json/encodeSummaryArticle.js
index 2fc5144..0b9461c 100644
--- a/packages/gitbook/lib/json/encodeSummaryArticle.js
+++ b/packages/gitbook/src/json/encodeSummaryArticle.js
@@ -6,7 +6,7 @@
     @return {Object}
 */
 function encodeSummaryArticle(article, recursive) {
-    var articles = undefined;
+    let articles = undefined;
     if (recursive !== false) {
         articles = article.getArticles()
             .map(encodeSummaryArticle)
@@ -21,7 +21,7 @@ function encodeSummaryArticle(article, recursive) {
         url: article.getUrl(),
         path: article.getPath(),
         ref: article.getRef(),
-        articles: articles
+        articles
     };
 }
 
diff --git a/packages/gitbook/lib/json/encodeSummaryPart.js b/packages/gitbook/src/json/encodeSummaryPart.js
index a5e7218..eb16719 100644
--- a/packages/gitbook/lib/json/encodeSummaryPart.js
+++ b/packages/gitbook/src/json/encodeSummaryPart.js
@@ -1,4 +1,4 @@
-var encodeSummaryArticle = require('./encodeSummaryArticle');
+const encodeSummaryArticle = require('./encodeSummaryArticle');
 
 /**
     Encode a SummaryPart to JSON
diff --git a/packages/gitbook/lib/json/index.js b/packages/gitbook/src/json/index.js
index 3b68f5e..3b68f5e 100644
--- a/packages/gitbook/lib/json/index.js
+++ b/packages/gitbook/src/json/index.js
diff --git a/packages/gitbook/lib/models/__tests__/config.js b/packages/gitbook/src/models/__tests__/config.js
index abad754..a865f96 100644
--- a/packages/gitbook/lib/models/__tests__/config.js
+++ b/packages/gitbook/src/models/__tests__/config.js
@@ -1,8 +1,8 @@
-var Immutable = require('immutable');
-var Config = require('../config');
+const Immutable = require('immutable');
+const Config = require('../config');
 
 describe('Config', function() {
-    var config = Config.createWithValues({
+    const config = Config.createWithValues({
         hello: {
             world: 1,
             test: 'Hello',
@@ -12,32 +12,32 @@ describe('Config', function() {
 
     describe('getValue', function() {
         it('must return value as immutable', function() {
-            var value = config.getValue('hello');
+            const value = config.getValue('hello');
             expect(Immutable.Map.isMap(value)).toBeTruthy();
         });
 
         it('must return deep value', function() {
-            var value = config.getValue('hello.world');
+            const value = config.getValue('hello.world');
             expect(value).toBe(1);
         });
 
         it('must return default value if non existant', function() {
-            var value = config.getValue('hello.nonExistant', 'defaultValue');
+            const value = config.getValue('hello.nonExistant', 'defaultValue');
             expect(value).toBe('defaultValue');
         });
 
         it('must not return default value for falsy values', function() {
-            var value = config.getValue('hello.isFalse', 'defaultValue');
+            const value = config.getValue('hello.isFalse', 'defaultValue');
             expect(value).toBe(false);
         });
     });
 
     describe('setValue', function() {
         it('must set value as immutable', function() {
-            var testConfig = config.setValue('hello', {
+            const testConfig = config.setValue('hello', {
                 'cool': 1
             });
-            var value = testConfig.getValue('hello');
+            const value = testConfig.getValue('hello');
 
             expect(Immutable.Map.isMap(value)).toBeTruthy();
             expect(value.size).toBe(1);
@@ -45,9 +45,9 @@ describe('Config', function() {
         });
 
         it('must set deep value', function() {
-            var testConfig = config.setValue('hello.world', 2);
-            var hello = testConfig.getValue('hello');
-            var world = testConfig.getValue('hello.world');
+            const testConfig = config.setValue('hello.world', 2);
+            const hello = testConfig.getValue('hello');
+            const world = testConfig.getValue('hello.world');
 
             expect(Immutable.Map.isMap(hello)).toBeTruthy();
             expect(hello.size).toBe(3);
@@ -58,11 +58,11 @@ describe('Config', function() {
 
     describe('toReducedVersion', function() {
         it('must only return diffs for simple values', function() {
-            var _config = Config.createWithValues({
+            const _config = Config.createWithValues({
                 gitbook: '3.0.0'
             });
 
-            var reducedVersion = _config.toReducedVersion();
+            const reducedVersion = _config.toReducedVersion();
 
             expect(reducedVersion.toJS()).toEqual({
                 gitbook: '3.0.0'
@@ -70,13 +70,13 @@ describe('Config', function() {
         });
 
         it('must only return diffs for deep values', function() {
-            var _config = Config.createWithValues({
+            const _config = Config.createWithValues({
                 structure: {
                     readme: 'intro.md'
                 }
             });
 
-            var reducedVersion = _config.toReducedVersion();
+            const reducedVersion = _config.toReducedVersion();
 
             expect(reducedVersion.toJS()).toEqual({
                 structure: {
@@ -87,4 +87,3 @@ describe('Config', function() {
     });
 });
 
-
diff --git a/packages/gitbook/lib/models/__tests__/glossary.js b/packages/gitbook/src/models/__tests__/glossary.js
index 5bf64dc..b50338a 100644
--- a/packages/gitbook/lib/models/__tests__/glossary.js
+++ b/packages/gitbook/src/models/__tests__/glossary.js
@@ -1,9 +1,9 @@
-var File = require('../file');
-var Glossary = require('../glossary');
-var GlossaryEntry = require('../glossaryEntry');
+const File = require('../file');
+const Glossary = require('../glossary');
+const GlossaryEntry = require('../glossaryEntry');
 
 describe('Glossary', function() {
-    var glossary = Glossary.createFromEntries(File(), [
+    const glossary = Glossary.createFromEntries(File(), [
         {
             name: 'Hello World',
             description: 'Awesome!'
@@ -16,13 +16,13 @@ describe('Glossary', function() {
 
     describe('createFromEntries', function() {
         it('must add all entries', function() {
-            var entries = glossary.getEntries();
+            const entries = glossary.getEntries();
             expect(entries.size).toBe(2);
         });
 
         it('must add entries as GlossaryEntries', function() {
-            var entries = glossary.getEntries();
-            var entry = entries.get('hello-world');
+            const entries = glossary.getEntries();
+            const entry = entries.get('hello-world');
             expect(entry instanceof GlossaryEntry).toBeTruthy();
         });
     });
@@ -37,4 +37,3 @@ describe('Glossary', function() {
     });
 });
 
-
diff --git a/packages/gitbook/lib/models/__tests__/glossaryEntry.js b/packages/gitbook/src/models/__tests__/glossaryEntry.js
index 833115d..66ddab4 100644
--- a/packages/gitbook/lib/models/__tests__/glossaryEntry.js
+++ b/packages/gitbook/src/models/__tests__/glossaryEntry.js
@@ -1,9 +1,9 @@
-var GlossaryEntry = require('../glossaryEntry');
+const GlossaryEntry = require('../glossaryEntry');
 
 describe('GlossaryEntry', function() {
     describe('getID', function() {
         it('must return a normalized ID', function() {
-            var entry = new GlossaryEntry({
+            const entry = new GlossaryEntry({
                 name: 'Hello World'
             });
 
@@ -12,4 +12,3 @@ describe('GlossaryEntry', function() {
     });
 });
 
-
diff --git a/packages/gitbook/lib/models/__tests__/page.js b/packages/gitbook/src/models/__tests__/page.js
index 479d276..ad9420e 100644
--- a/packages/gitbook/lib/models/__tests__/page.js
+++ b/packages/gitbook/src/models/__tests__/page.js
@@ -1,11 +1,11 @@
-var Immutable = require('immutable');
-var Page = require('../page');
+const Immutable = require('immutable');
+const Page = require('../page');
 
 describe('Page', function() {
 
     describe('toText', function() {
         it('must not prepend frontmatter if no attributes', function() {
-            var page = Page().merge({
+            const page = Page().merge({
                 content: 'Hello World'
             });
 
@@ -13,7 +13,7 @@ describe('Page', function() {
         });
 
         it('must prepend frontmatter if attributes', function() {
-            var page = Page().merge({
+            const page = Page().merge({
                 content: 'Hello World',
                 attributes: Immutable.fromJS({
                     hello: 'world'
@@ -25,4 +25,3 @@ describe('Page', function() {
     });
 });
 
-
diff --git a/packages/gitbook/lib/models/__tests__/plugin.js b/packages/gitbook/src/models/__tests__/plugin.js
index b229664..63cb58c 100644
--- a/packages/gitbook/lib/models/__tests__/plugin.js
+++ b/packages/gitbook/src/models/__tests__/plugin.js
@@ -1,15 +1,15 @@
 describe('Plugin', function() {
-    var Plugin = require('../plugin');
+    const Plugin = require('../plugin');
 
     describe('createFromString', function() {
         it('must parse name', function() {
-            var plugin = Plugin.createFromString('hello');
+            const plugin = Plugin.createFromString('hello');
             expect(plugin.getName()).toBe('hello');
             expect(plugin.getVersion()).toBe('*');
         });
 
         it('must parse version', function() {
-            var plugin = Plugin.createFromString('hello@1.0.0');
+            const plugin = Plugin.createFromString('hello@1.0.0');
             expect(plugin.getName()).toBe('hello');
             expect(plugin.getVersion()).toBe('1.0.0');
         });
@@ -17,11 +17,10 @@ describe('Plugin', function() {
 
     describe('isLoaded', function() {
         it('must return false for empty plugin', function() {
-            var plugin = Plugin.createFromString('hello');
+            const plugin = Plugin.createFromString('hello');
             expect(plugin.isLoaded()).toBe(false);
         });
 
     });
 });
 
-
diff --git a/packages/gitbook/lib/models/__tests__/pluginDependency.js b/packages/gitbook/src/models/__tests__/pluginDependency.js
index cb04cf2..cda0cc2 100644
--- a/packages/gitbook/lib/models/__tests__/pluginDependency.js
+++ b/packages/gitbook/src/models/__tests__/pluginDependency.js
@@ -1,29 +1,29 @@
-var Immutable = require('immutable');
-var PluginDependency = require('../pluginDependency');
+const Immutable = require('immutable');
+const PluginDependency = require('../pluginDependency');
 
 describe('PluginDependency', function() {
     describe('createFromString', function() {
         it('must parse name', function() {
-            var plugin = PluginDependency.createFromString('hello');
+            const plugin = PluginDependency.createFromString('hello');
             expect(plugin.getName()).toBe('hello');
             expect(plugin.getVersion()).toBe('*');
         });
 
         it('must parse state', function() {
-            var plugin = PluginDependency.createFromString('-hello');
+            const plugin = PluginDependency.createFromString('-hello');
             expect(plugin.getName()).toBe('hello');
             expect(plugin.isEnabled()).toBe(false);
         });
 
         describe('Version', function() {
             it('must parse version', function() {
-                var plugin = PluginDependency.createFromString('hello@1.0.0');
+                const plugin = PluginDependency.createFromString('hello@1.0.0');
                 expect(plugin.getName()).toBe('hello');
                 expect(plugin.getVersion()).toBe('1.0.0');
             });
 
             it('must parse semver', function() {
-                var plugin = PluginDependency.createFromString('hello@>=4.0.0');
+                const plugin = PluginDependency.createFromString('hello@>=4.0.0');
                 expect(plugin.getName()).toBe('hello');
                 expect(plugin.getVersion()).toBe('>=4.0.0');
             });
@@ -31,13 +31,13 @@ describe('PluginDependency', function() {
 
         describe('GIT Version', function() {
             it('must handle HTTPS urls', function() {
-                var plugin = PluginDependency.createFromString('hello@git+https://github.com/GitbookIO/plugin-ga.git');
+                const plugin = PluginDependency.createFromString('hello@git+https://github.com/GitbookIO/plugin-ga.git');
                 expect(plugin.getName()).toBe('hello');
                 expect(plugin.getVersion()).toBe('git+https://github.com/GitbookIO/plugin-ga.git');
             });
 
             it('must handle SSH urls', function() {
-                var plugin = PluginDependency.createFromString('hello@git+ssh://samy@github.com/GitbookIO/plugin-ga.git');
+                const plugin = PluginDependency.createFromString('hello@git+ssh://samy@github.com/GitbookIO/plugin-ga.git');
                 expect(plugin.getName()).toBe('hello');
                 expect(plugin.getVersion()).toBe('git+ssh://samy@github.com/GitbookIO/plugin-ga.git');
             });
@@ -45,7 +45,7 @@ describe('PluginDependency', function() {
 
         describe('listToArray', function() {
             it('must create an array from a list of plugin dependencies', function() {
-                var list = PluginDependency.listToArray(Immutable.List([
+                const list = PluginDependency.listToArray(Immutable.List([
                     PluginDependency.createFromString('hello@1.0.0'),
                     PluginDependency.createFromString('noversion'),
                     PluginDependency.createFromString('-disabled')
@@ -61,14 +61,14 @@ describe('PluginDependency', function() {
 
         describe('listFromArray', function() {
             it('must create an array from a list of plugin dependencies', function() {
-                var arr = Immutable.fromJS([
+                const arr = Immutable.fromJS([
                     'hello@1.0.0',
                     {
                         'name': 'plugin-ga',
                         'version': 'git+ssh://samy@github.com/GitbookIO/plugin-ga.git'
                     }
                 ]);
-                var list = PluginDependency.listFromArray(arr);
+                const list = PluginDependency.listFromArray(arr);
 
                 expect(list.first().getName()).toBe('hello');
                 expect(list.first().getVersion()).toBe('1.0.0');
diff --git a/packages/gitbook/lib/models/__tests__/summary.js b/packages/gitbook/src/models/__tests__/summary.js
index 29c9330..49ed9b1 100644
--- a/packages/gitbook/lib/models/__tests__/summary.js
+++ b/packages/gitbook/src/models/__tests__/summary.js
@@ -1,9 +1,9 @@
 
 describe('Summary', function() {
-    var File = require('../file');
-    var Summary = require('../summary');
+    const File = require('../file');
+    const Summary = require('../summary');
 
-    var summary = Summary.createFromParts(File(), [
+    const summary = Summary.createFromParts(File(), [
         {
             articles: [
                 {
@@ -30,21 +30,21 @@ describe('Summary', function() {
 
     describe('createFromEntries', function() {
         it('must add all parts', function() {
-            var parts = summary.getParts();
+            const parts = summary.getParts();
             expect(parts.size).toBe(2);
         });
     });
 
     describe('getByLevel', function() {
         it('can return a Part', function() {
-            var part = summary.getByLevel('1');
+            const part = summary.getByLevel('1');
 
             expect(part).toBeDefined();
             expect(part.getArticles().size).toBe(4);
         });
 
         it('can return a Part (2)', function() {
-            var part = summary.getByLevel('2');
+            const part = summary.getByLevel('2');
 
             expect(part).toBeDefined();
             expect(part.getTitle()).toBe('Test');
@@ -52,7 +52,7 @@ describe('Summary', function() {
         });
 
         it('can return an Article', function() {
-            var article = summary.getByLevel('1.1');
+            const article = summary.getByLevel('1.1');
 
             expect(article).toBeDefined();
             expect(article.getTitle()).toBe('My First Article');
@@ -61,21 +61,21 @@ describe('Summary', function() {
 
     describe('getByPath', function() {
         it('return correct article', function() {
-            var article = summary.getByPath('README.md');
+            const article = summary.getByPath('README.md');
 
             expect(article).toBeDefined();
             expect(article.getTitle()).toBe('My First Article');
         });
 
         it('return correct article', function() {
-            var article = summary.getByPath('article.md');
+            const article = summary.getByPath('article.md');
 
             expect(article).toBeDefined();
             expect(article.getTitle()).toBe('My Second Article');
         });
 
         it('return undefined if not found', function() {
-            var article = summary.getByPath('NOT_EXISTING.md');
+            const article = summary.getByPath('NOT_EXISTING.md');
 
             expect(article).toBeFalsy();
         });
@@ -91,4 +91,3 @@ describe('Summary', function() {
     });
 });
 
-
diff --git a/packages/gitbook/lib/models/__tests__/summaryArticle.js b/packages/gitbook/src/models/__tests__/summaryArticle.js
index 22a7a20..506d481 100644
--- a/packages/gitbook/lib/models/__tests__/summaryArticle.js
+++ b/packages/gitbook/src/models/__tests__/summaryArticle.js
@@ -1,15 +1,15 @@
-var SummaryArticle = require('../summaryArticle');
-var File = require('../file');
+const SummaryArticle = require('../summaryArticle');
+const File = require('../file');
 
 describe('SummaryArticle', function() {
     describe('createChildLevel', function() {
         it('must create the right level', function() {
-            var article = SummaryArticle.create({}, '1.1');
+            const article = SummaryArticle.create({}, '1.1');
             expect(article.createChildLevel()).toBe('1.1.1');
         });
 
         it('must create the right level when has articles', function() {
-            var article = SummaryArticle.create({
+            const article = SummaryArticle.create({
                 articles: [
                     {
                         title: 'Test'
@@ -22,32 +22,31 @@ describe('SummaryArticle', function() {
 
     describe('isFile', function() {
         it('must return true when exactly the file', function() {
-            var article = SummaryArticle.create({
+            const article = SummaryArticle.create({
                 ref: 'hello.md'
             }, '1.1');
-            var file = File.createWithFilepath('hello.md');
+            const file = File.createWithFilepath('hello.md');
 
             expect(article.isFile(file)).toBe(true);
         });
 
         it('must return true when path is not normalized', function() {
-            var article = SummaryArticle.create({
+            const article = SummaryArticle.create({
                 ref: '/hello.md'
             }, '1.1');
-            var file = File.createWithFilepath('hello.md');
+            const file = File.createWithFilepath('hello.md');
 
             expect(article.isFile(file)).toBe(true);
         });
 
         it('must return false when has anchor', function() {
-            var article = SummaryArticle.create({
+            const article = SummaryArticle.create({
                 ref: 'hello.md#world'
             }, '1.1');
-            var file = File.createWithFilepath('hello.md');
+            const file = File.createWithFilepath('hello.md');
 
             expect(article.isFile(file)).toBe(false);
         });
     });
 });
 
-
diff --git a/packages/gitbook/lib/models/__tests__/summaryPart.js b/packages/gitbook/src/models/__tests__/summaryPart.js
index 8ee50b6..fc9e8b5 100644
--- a/packages/gitbook/lib/models/__tests__/summaryPart.js
+++ b/packages/gitbook/src/models/__tests__/summaryPart.js
@@ -1,14 +1,14 @@
-var SummaryPart = require('../summaryPart');
+const SummaryPart = require('../summaryPart');
 
 describe('SummaryPart', function() {
     describe('createChildLevel', function() {
         it('must create the right level', function() {
-            var article = SummaryPart.create({}, '1');
+            const article = SummaryPart.create({}, '1');
             expect(article.createChildLevel()).toBe('1.1');
         });
 
         it('must create the right level when has articles', function() {
-            var article = SummaryPart.create({
+            const article = SummaryPart.create({
                 articles: [
                     {
                         title: 'Test'
@@ -20,4 +20,3 @@ describe('SummaryPart', function() {
     });
 });
 
-
diff --git a/packages/gitbook/lib/models/__tests__/templateBlock.js b/packages/gitbook/src/models/__tests__/templateBlock.js
index e5f7666..20511be 100644
--- a/packages/gitbook/lib/models/__tests__/templateBlock.js
+++ b/packages/gitbook/src/models/__tests__/templateBlock.js
@@ -1,13 +1,13 @@
-var nunjucks = require('nunjucks');
-var Immutable = require('immutable');
-var Promise = require('../../utils/promise');
+const nunjucks = require('nunjucks');
+const Immutable = require('immutable');
+const Promise = require('../../utils/promise');
 
 describe('TemplateBlock', function() {
-    var TemplateBlock = require('../templateBlock');
+    const TemplateBlock = require('../templateBlock');
 
     describe('create', function() {
         it('must initialize a simple TemplateBlock from a function', function() {
-            var templateBlock = TemplateBlock.create('sayhello', function(block) {
+            const templateBlock = TemplateBlock.create('sayhello', function(block) {
                 return {
                     body: '<p>Hello, World!</p>',
                     parse: true
@@ -34,7 +34,7 @@ describe('TemplateBlock', function() {
 
     describe('getShortcuts', function() {
         it('must return undefined if no shortcuts', function() {
-            var templateBlock = TemplateBlock.create('sayhello', function(block) {
+            const templateBlock = TemplateBlock.create('sayhello', function(block) {
                 return {
                     body: '<p>Hello, World!</p>',
                     parse: true
@@ -45,8 +45,8 @@ describe('TemplateBlock', function() {
         });
 
         it('must return complete shortcut', function() {
-            var templateBlock = TemplateBlock.create('sayhello', {
-                process: function(block) {
+            const templateBlock = TemplateBlock.create('sayhello', {
+                process(block) {
                     return '<p>Hello, World!</p>';
                 },
                 shortcuts: {
@@ -56,7 +56,7 @@ describe('TemplateBlock', function() {
                 }
             });
 
-            var shortcut = templateBlock.getShortcuts();
+            const shortcut = templateBlock.getShortcuts();
 
             expect(shortcut).toBeDefined();
             expect(shortcut.getStart()).toEqual('$');
@@ -68,28 +68,28 @@ describe('TemplateBlock', function() {
 
     describe('toNunjucksExt()', function() {
         it('should replace by block anchor', function() {
-            var templateBlock = TemplateBlock.create('sayhello', function(block) {
+            const templateBlock = TemplateBlock.create('sayhello', function(block) {
                 return 'Hello';
             });
 
-            var blocks = {};
+            let blocks = {};
 
             // Create a fresh Nunjucks environment
-            var env = new nunjucks.Environment(null, { autoescape: false });
+            const env = new nunjucks.Environment(null, { autoescape: false });
 
             // Add template block to environement
-            var Ext = templateBlock.toNunjucksExt({}, blocks);
+            const Ext = templateBlock.toNunjucksExt({}, blocks);
             env.addExtension(templateBlock.getExtensionName(), new Ext());
 
             // Render a template using the block
-            var src = '{% sayhello %}{% endsayhello %}';
+            const src = '{% sayhello %}{% endsayhello %}';
             return Promise.nfcall(env.renderString.bind(env), src)
             .then(function(res) {
                 blocks = Immutable.fromJS(blocks);
                 expect(blocks.size).toBe(1);
 
-                var blockId = blocks.keySeq().get(0);
-                var block = blocks.get(blockId);
+                const blockId = blocks.keySeq().get(0);
+                const block = blocks.get(blockId);
 
                 expect(res).toBe('{{-%' + blockId + '%-}}');
                 expect(block.get('body')).toBe('Hello');
@@ -98,7 +98,7 @@ describe('TemplateBlock', function() {
         });
 
         it('must create a valid nunjucks extension', function() {
-            var templateBlock = TemplateBlock.create('sayhello', function(block) {
+            const templateBlock = TemplateBlock.create('sayhello', function(block) {
                 return {
                     body: '<p>Hello, World!</p>',
                     parse: true
@@ -106,14 +106,14 @@ describe('TemplateBlock', function() {
             });
 
             // Create a fresh Nunjucks environment
-            var env = new nunjucks.Environment(null, { autoescape: false });
+            const env = new nunjucks.Environment(null, { autoescape: false });
 
             // Add template block to environement
-            var Ext = templateBlock.toNunjucksExt();
+            const Ext = templateBlock.toNunjucksExt();
             env.addExtension(templateBlock.getExtensionName(), new Ext());
 
             // Render a template using the block
-            var src = '{% sayhello %}{% endsayhello %}';
+            const src = '{% sayhello %}{% endsayhello %}';
             return Promise.nfcall(env.renderString.bind(env), src)
             .then(function(res) {
                 expect(res).toBe('<p>Hello, World!</p>');
@@ -121,22 +121,22 @@ describe('TemplateBlock', function() {
         });
 
         it('must apply block arguments correctly', function() {
-            var templateBlock = TemplateBlock.create('sayhello', function(block) {
+            const templateBlock = TemplateBlock.create('sayhello', function(block) {
                 return {
-                    body: '<'+block.kwargs.tag+'>Hello, '+block.kwargs.name+'!</'+block.kwargs.tag+'>',
+                    body: '<' + block.kwargs.tag + '>Hello, ' + block.kwargs.name + '!</' + block.kwargs.tag + '>',
                     parse: true
                 };
             });
 
             // Create a fresh Nunjucks environment
-            var env = new nunjucks.Environment(null, { autoescape: false });
+            const env = new nunjucks.Environment(null, { autoescape: false });
 
             // Add template block to environement
-            var Ext = templateBlock.toNunjucksExt();
+            const Ext = templateBlock.toNunjucksExt();
             env.addExtension(templateBlock.getExtensionName(), new Ext());
 
             // Render a template using the block
-            var src = '{% sayhello name="Samy", tag="p" %}{% endsayhello %}';
+            const src = '{% sayhello name="Samy", tag="p" %}{% endsayhello %}';
             return Promise.nfcall(env.renderString.bind(env), src)
             .then(function(res) {
                 expect(res).toBe('<p>Hello, Samy!</p>');
@@ -144,7 +144,7 @@ describe('TemplateBlock', function() {
         });
 
         it('must accept an async function', function() {
-            var templateBlock = TemplateBlock.create('sayhello', function(block) {
+            const templateBlock = TemplateBlock.create('sayhello', function(block) {
                 return Promise()
                 .then(function() {
                     return {
@@ -155,14 +155,14 @@ describe('TemplateBlock', function() {
             });
 
             // Create a fresh Nunjucks environment
-            var env = new nunjucks.Environment(null, { autoescape: false });
+            const env = new nunjucks.Environment(null, { autoescape: false });
 
             // Add template block to environement
-            var Ext = templateBlock.toNunjucksExt();
+            const Ext = templateBlock.toNunjucksExt();
             env.addExtension(templateBlock.getExtensionName(), new Ext());
 
             // Render a template using the block
-            var src = '{% sayhello %}Samy{% endsayhello %}';
+            const src = '{% sayhello %}Samy{% endsayhello %}';
             return Promise.nfcall(env.renderString.bind(env), src)
             .then(function(res) {
                 expect(res).toBe('Hello Samy');
@@ -170,36 +170,36 @@ describe('TemplateBlock', function() {
         });
 
         it('must handle nested blocks', function() {
-            var templateBlock = new TemplateBlock({
+            const templateBlock = new TemplateBlock({
                 name: 'yoda',
                 blocks: Immutable.List(['start', 'end']),
-                process: function(block) {
-                    var nested = {};
+                process(block) {
+                    const nested = {};
 
                     block.blocks.forEach(function(blk) {
                         nested[blk.name] = blk.body.trim();
                     });
 
                     return {
-                        body: '<p class="yoda">'+nested.end+' '+nested.start+'</p>',
+                        body: '<p class="yoda">' + nested.end + ' ' + nested.start + '</p>',
                         parse: true
                     };
                 }
             });
 
             // Create a fresh Nunjucks environment
-            var env = new nunjucks.Environment(null, { autoescape: false });
+            const env = new nunjucks.Environment(null, { autoescape: false });
 
             // Add template block to environement
-            var Ext = templateBlock.toNunjucksExt();
+            const Ext = templateBlock.toNunjucksExt();
             env.addExtension(templateBlock.getExtensionName(), new Ext());
 
             // Render a template using the block
-            var src = '{% yoda %}{% start %}this sentence should be{% end %}inverted{% endyoda %}';
+            const src = '{% yoda %}{% start %}this sentence should be{% end %}inverted{% endyoda %}';
             return Promise.nfcall(env.renderString.bind(env), src)
             .then(function(res) {
                 expect(res).toBe('<p class="yoda">inverted this sentence should be</p>');
             });
         });
     });
-});
\ No newline at end of file
+});
diff --git a/packages/gitbook/lib/models/__tests__/templateEngine.js b/packages/gitbook/src/models/__tests__/templateEngine.js
index 6f18b18..30cd543 100644
--- a/packages/gitbook/lib/models/__tests__/templateEngine.js
+++ b/packages/gitbook/src/models/__tests__/templateEngine.js
@@ -1,40 +1,40 @@
 
 describe('TemplateBlock', function() {
-    var TemplateEngine = require('../templateEngine');
+    const TemplateEngine = require('../templateEngine');
 
     describe('create', function() {
         it('must initialize with a list of filters', function() {
-            var engine = TemplateEngine.create({
+            const engine = TemplateEngine.create({
                 filters: {
-                    hello: function(name) {
+                    hello(name) {
                         return 'Hello ' + name + '!';
                     }
                 }
             });
-            var env = engine.toNunjucks();
-            var res = env.renderString('{{ "Luke"|hello }}');
+            const env = engine.toNunjucks();
+            const res = env.renderString('{{ "Luke"|hello }}');
 
             expect(res).toBe('Hello Luke!');
         });
 
         it('must initialize with a list of globals', function() {
-            var engine = TemplateEngine.create({
+            const engine = TemplateEngine.create({
                 globals: {
-                    hello: function(name) {
+                    hello(name) {
                         return 'Hello ' + name + '!';
                     }
                 }
             });
-            var env = engine.toNunjucks();
-            var res = env.renderString('{{ hello("Luke") }}');
+            const env = engine.toNunjucks();
+            const res = env.renderString('{{ hello("Luke") }}');
 
             expect(res).toBe('Hello Luke!');
         });
 
         it('must pass context to filters and blocks', function() {
-            var engine = TemplateEngine.create({
+            const engine = TemplateEngine.create({
                 filters: {
-                    hello: function(name) {
+                    hello(name) {
                         return 'Hello ' + name + ' ' + this.lastName + '!';
                     }
                 },
@@ -42,10 +42,10 @@ describe('TemplateBlock', function() {
                     lastName: 'Skywalker'
                 }
             });
-            var env = engine.toNunjucks();
-            var res = env.renderString('{{ "Luke"|hello }}');
+            const env = engine.toNunjucks();
+            const res = env.renderString('{{ "Luke"|hello }}');
 
             expect(res).toBe('Hello Luke Skywalker!');
         });
     });
-});
\ No newline at end of file
+});
diff --git a/packages/gitbook/lib/models/book.js b/packages/gitbook/src/models/book.js
index f774ee8..4164536 100644
--- a/packages/gitbook/lib/models/book.js
+++ b/packages/gitbook/src/models/book.js
@@ -1,17 +1,17 @@
-var path = require('path');
-var Immutable = require('immutable');
+const path = require('path');
+const Immutable = require('immutable');
 
-var Logger = require('../utils/logger');
+const Logger = require('../utils/logger');
 
-var FS = require('./fs');
-var Config = require('./config');
-var Readme = require('./readme');
-var Summary = require('./summary');
-var Glossary = require('./glossary');
-var Languages = require('./languages');
-var Ignore = require('./ignore');
+const FS = require('./fs');
+const Config = require('./config');
+const Readme = require('./readme');
+const Summary = require('./summary');
+const Glossary = require('./glossary');
+const Languages = require('./languages');
+const Ignore = require('./ignore');
 
-var Book = Immutable.Record({
+const Book = Immutable.Record({
     // Logger for outptu message
     logger:         Logger(),
 
@@ -81,9 +81,9 @@ Book.prototype.getLanguage = function() {
     @return {FS}
 */
 Book.prototype.getContentFS = function() {
-    var fs = this.getFS();
-    var config = this.getConfig();
-    var rootFolder = config.getValue('root');
+    const fs = this.getFS();
+    const config = this.getConfig();
+    const rootFolder = config.getValue('root');
 
     if (rootFolder) {
         return FS.reduceScope(fs, rootFolder);
@@ -98,7 +98,7 @@ Book.prototype.getContentFS = function() {
     @return {String}
 */
 Book.prototype.getRoot = function() {
-    var fs = this.getFS();
+    const fs = this.getFS();
     return fs.getRoot();
 };
 
@@ -108,7 +108,7 @@ Book.prototype.getRoot = function() {
     @return {String}
 */
 Book.prototype.getContentRoot = function() {
-    var fs = this.getContentFS();
+    const fs = this.getContentFS();
     return fs.getRoot();
 };
 
@@ -119,8 +119,8 @@ Book.prototype.getContentRoot = function() {
     @return {Page|undefined}
 */
 Book.prototype.isFileIgnored = function(filename) {
-    var ignore = this.getIgnore();
-    var language = this.getLanguage();
+    const ignore = this.getIgnore();
+    const language = this.getLanguage();
 
     // Ignore is always relative to the root of the main book
     if (language) {
@@ -137,8 +137,8 @@ Book.prototype.isFileIgnored = function(filename) {
     @return {Page|undefined}
 */
 Book.prototype.isContentFileIgnored = function(filename) {
-    var config = this.getConfig();
-    var rootFolder = config.getValue('root');
+    const config = this.getConfig();
+    const rootFolder = config.getValue('root');
 
     if (rootFolder) {
         filename = path.join(rootFolder, filename);
@@ -182,7 +182,7 @@ Book.prototype.isLanguageBook = function() {
     @return {Book}
 */
 Book.prototype.getLanguageBook = function(language) {
-    var books = this.getBooks();
+    const books = this.getBooks();
     return books.get(language);
 };
 
@@ -194,7 +194,7 @@ Book.prototype.getLanguageBook = function(language) {
     @return {Book}
 */
 Book.prototype.addLanguageBook = function(language, book) {
-    var books = this.getBooks();
+    let books = this.getBooks();
     books = books.set(language, book);
 
     return this.set('books', books);
@@ -259,7 +259,7 @@ Book.prototype.setLogLevel = function(level) {
 */
 Book.createForFS = function createForFS(fs) {
     return new Book({
-        fs: fs
+        fs
     });
 };
 
@@ -269,15 +269,15 @@ Book.createForFS = function createForFS(fs) {
 */
 Book.prototype.getDefaultExt = function() {
     // Inferring sources
-    var clues = [
+    const clues = [
         this.getReadme(),
         this.getSummary(),
         this.getGlossary()
     ];
 
     // List their extensions
-    var exts = clues.map(function (clue) {
-        var file = clue.getFile();
+    const exts = clues.map(function(clue) {
+        const file = clue.getFile();
         if (file.exists()) {
             return file.getParser().getExtensions().first();
         } else {
@@ -288,7 +288,7 @@ Book.prototype.getDefaultExt = function() {
     exts.push('.md');
 
     // Choose the first non null
-    return exts.find(function (e) { return e !== null; });
+    return exts.find(function(e) { return e !== null; });
 };
 
 /**
@@ -298,7 +298,7 @@ Book.prototype.getDefaultExt = function() {
     @return {String}
 */
 Book.prototype.getDefaultReadmePath = function(absolute) {
-    var defaultPath = 'README'+this.getDefaultExt();
+    const defaultPath = 'README' + this.getDefaultExt();
     if (absolute) {
         return path.join(this.getContentRoot(), defaultPath);
     } else {
@@ -313,7 +313,7 @@ Book.prototype.getDefaultReadmePath = function(absolute) {
     @return {String}
 */
 Book.prototype.getDefaultSummaryPath = function(absolute) {
-    var defaultPath = 'SUMMARY'+this.getDefaultExt();
+    const defaultPath = 'SUMMARY' + this.getDefaultExt();
     if (absolute) {
         return path.join(this.getContentRoot(), defaultPath);
     } else {
@@ -328,7 +328,7 @@ Book.prototype.getDefaultSummaryPath = function(absolute) {
     @return {String}
 */
 Book.prototype.getDefaultGlossaryPath = function(absolute) {
-    var defaultPath = 'GLOSSARY'+this.getDefaultExt();
+    const defaultPath = 'GLOSSARY' + this.getDefaultExt();
     if (absolute) {
         return path.join(this.getContentRoot(), defaultPath);
     } else {
@@ -344,8 +344,8 @@ Book.prototype.getDefaultGlossaryPath = function(absolute) {
     @return {Book}
 */
 Book.createFromParent = function createFromParent(parent, language) {
-    var ignore = parent.getIgnore();
-    var config = parent.getConfig();
+    const ignore = parent.getIgnore();
+    let config = parent.getConfig();
 
     // Set language in configuration
     config = config.setValue('language', language);
@@ -353,10 +353,10 @@ Book.createFromParent = function createFromParent(parent, language) {
     return new Book({
         // Inherits config. logegr and list of ignored files
         logger: parent.getLogger(),
-        config: config,
-        ignore: ignore,
+        config,
+        ignore,
 
-        language: language,
+        language,
         fs: FS.reduceScope(parent.getContentFS(), language)
     });
 };
diff --git a/packages/gitbook/lib/models/config.js b/packages/gitbook/src/models/config.js
index 6de52f9..6a0be5e 100644
--- a/packages/gitbook/lib/models/config.js
+++ b/packages/gitbook/src/models/config.js
@@ -1,12 +1,12 @@
-var is = require('is');
-var Immutable = require('immutable');
+const is = require('is');
+const Immutable = require('immutable');
 
-var File = require('./file');
-var PluginDependency = require('./pluginDependency');
-var configDefault = require('../constants/configDefault');
-var reducedObject = require('../utils/reducedObject');
+const File = require('./file');
+const PluginDependency = require('./pluginDependency');
+const configDefault = require('../constants/configDefault');
+const reducedObject = require('../utils/reducedObject');
 
-var Config = Immutable.Record({
+const Config = Immutable.Record({
     file:       File(),
     values:     configDefault
 }, 'Config');
@@ -51,7 +51,7 @@ Config.prototype.setFile = function(file) {
  * @return {Mixed}
  */
 Config.prototype.getValue = function(keyPath, def) {
-    var values = this.getValues();
+    const values = this.getValues();
     keyPath = Config.keyToKeyPath(keyPath);
 
     if (!values.hasIn(keyPath)) {
@@ -72,7 +72,7 @@ Config.prototype.setValue = function(keyPath, value) {
 
     value = Immutable.fromJS(value);
 
-    var values = this.getValues();
+    let values = this.getValues();
     values = values.setIn(keyPath, value);
 
     return this.set('values', values);
@@ -83,7 +83,7 @@ Config.prototype.setValue = function(keyPath, value) {
  * @return {List<PluginDependency>}
  */
 Config.prototype.getPluginDependencies = function() {
-    var plugins = this.getValue('plugins');
+    const plugins = this.getValue('plugins');
 
     if (is.string(plugins)) {
         return PluginDependency.listFromString(plugins);
@@ -98,7 +98,7 @@ Config.prototype.getPluginDependencies = function() {
  * @return {PluginDependency}
  */
 Config.prototype.getPluginDependency = function(name) {
-    var plugins = this.getPluginDependencies();
+    const plugins = this.getPluginDependencies();
 
     return plugins.find(function(dep) {
         return dep.getName() === name;
@@ -111,7 +111,7 @@ Config.prototype.getPluginDependency = function(name) {
  * @return {Config}
  */
 Config.prototype.setPluginDependencies = function(deps) {
-    var plugins = PluginDependency.listToArray(deps);
+    const plugins = PluginDependency.listToArray(deps);
 
     return this.setValue('plugins', plugins);
 };
@@ -135,7 +135,7 @@ Config.prototype.updateValues = function(values) {
  * @returns {Config}
  */
 Config.prototype.mergeValues = function(values) {
-    var currentValues = this.getValues();
+    let currentValues = this.getValues();
     values = Immutable.fromJS(values);
 
     currentValues = currentValues.mergeDeep(values);
@@ -151,7 +151,7 @@ Config.prototype.mergeValues = function(values) {
  */
 Config.create = function(file, values) {
     return new Config({
-        file: file,
+        file,
         values: Immutable.fromJS(values)
     });
 };
diff --git a/packages/gitbook/lib/models/file.js b/packages/gitbook/src/models/file.js
index 8ddd4af..84828ce 100644
--- a/packages/gitbook/lib/models/file.js
+++ b/packages/gitbook/src/models/file.js
@@ -1,9 +1,9 @@
-var path = require('path');
-var Immutable = require('immutable');
+const path = require('path');
+const Immutable = require('immutable');
 
-var parsers = require('../parsers');
+const parsers = require('../parsers');
 
-var File = Immutable.Record({
+const File = Immutable.Record({
     // Path of the file, relative to the FS
     path:       String(),
 
@@ -34,7 +34,7 @@ File.prototype.exists = function() {
     @return {String}
 */
 File.prototype.getType = function() {
-    var parser = this.getParser();
+    const parser = this.getParser();
     if (parser) {
         return parser.getName();
     } else {
diff --git a/packages/gitbook/lib/models/fs.js b/packages/gitbook/src/models/fs.js
index 16bd4ea..7afbfbd 100644
--- a/packages/gitbook/lib/models/fs.js
+++ b/packages/gitbook/src/models/fs.js
@@ -1,13 +1,13 @@
-var path = require('path');
-var Immutable = require('immutable');
-var stream = require('stream');
+const path = require('path');
+const Immutable = require('immutable');
+const stream = require('stream');
 
-var File = require('./file');
-var Promise = require('../utils/promise');
-var error = require('../utils/error');
-var PathUtil = require('../utils/path');
+const File = require('./file');
+const Promise = require('../utils/promise');
+const error = require('../utils/error');
+const PathUtil = require('../utils/path');
 
-var FS = Immutable.Record({
+const FS = Immutable.Record({
     root:           String(),
 
     fsExists:         Function(),
@@ -35,27 +35,25 @@ FS.prototype.getRoot = function() {
     @return {Boolean}
 */
 FS.prototype.isInScope = function(filename) {
-    var rootPath = this.getRoot();
+    const rootPath = this.getRoot();
     filename = path.join(rootPath, filename);
 
     return PathUtil.isInRoot(rootPath, filename);
 };
 
 /**
-    Resolve a file in this FS
-
-    @param {String}
-    @return {String}
-*/
-FS.prototype.resolve = function() {
-    var rootPath = this.getRoot();
-    var args = Array.prototype.slice.call(arguments);
-    var filename = path.join.apply(path, [rootPath].concat(args));
+ * Resolve a file in this FS
+ * @param {String}
+ * @return {String}
+ */
+FS.prototype.resolve = function(...args) {
+    const rootPath = this.getRoot();
+    let filename = path.join(rootPath, ...args);
     filename = path.normalize(filename);
 
     if (!this.isInScope(filename)) {
         throw error.FileOutOfScopeError({
-            filename: filename,
+            filename,
             root: this.root
         });
     }
@@ -64,47 +62,44 @@ FS.prototype.resolve = function() {
 };
 
 /**
-    Check if a file exists, run a Promise(true) if that's the case, Promise(false) otherwise
-
-    @param {String} filename
-    @return {Promise<Boolean>}
-*/
+ * Check if a file exists, run a Promise(true) if that's the case, Promise(false) otherwise
+ * @param {String} filename
+ * @return {Promise<Boolean>}
+ */
 FS.prototype.exists = function(filename) {
-    var that = this;
+    const that = this;
 
     return Promise()
     .then(function() {
         filename = that.resolve(filename);
-        var exists = that.get('fsExists');
+        const exists = that.get('fsExists');
 
         return exists(filename);
     });
 };
 
 /**
-    Read a file and returns a promise with the content as a buffer
-
-    @param {String} filename
-    @return {Promise<Buffer>}
-*/
+ * Read a file and returns a promise with the content as a buffer
+ * @param {String} filename
+ * @return {Promise<Buffer>}
+ */
 FS.prototype.read = function(filename) {
-    var that = this;
+    const that = this;
 
     return Promise()
     .then(function() {
         filename = that.resolve(filename);
-        var read = that.get('fsReadFile');
+        const read = that.get('fsReadFile');
 
         return read(filename);
     });
 };
 
 /**
-    Read a file as a string (utf-8)
-
-    @param {String} filename
-    @return {Promise<String>}
-*/
+ * Read a file as a string (utf-8)
+ * @param {String} filename
+ * @return {Promise<String>}
+ */
 FS.prototype.readAsString = function(filename, encoding) {
     encoding = encoding || 'utf8';
 
@@ -115,15 +110,14 @@ FS.prototype.readAsString = function(filename, encoding) {
 };
 
 /**
-    Read file as a stream
-
-    @param {String} filename
-    @return {Promise<Stream>}
-*/
+ * Read file as a stream
+ * @param {String} filename
+ * @return {Promise<Stream>}
+ */
 FS.prototype.readAsStream = function(filename) {
-    var that = this;
-    var filepath = that.resolve(filename);
-    var fsReadAsStream = this.get('fsReadAsStream');
+    const that = this;
+    const filepath = that.resolve(filename);
+    const fsReadAsStream = this.get('fsReadAsStream');
 
     if (fsReadAsStream) {
         return Promise(fsReadAsStream(filepath));
@@ -131,7 +125,7 @@ FS.prototype.readAsStream = function(filename) {
 
     return this.read(filename)
     .then(function(buf) {
-        var bufferStream = new stream.PassThrough();
+        const bufferStream = new stream.PassThrough();
         bufferStream.end(buf);
 
         return bufferStream;
@@ -139,18 +133,17 @@ FS.prototype.readAsStream = function(filename) {
 };
 
 /**
-    Read stat infos about a file
-
-    @param {String} filename
-    @return {Promise<File>}
-*/
+ * Read stat infos about a file
+ * @param {String} filename
+ * @return {Promise<File>}
+ */
 FS.prototype.statFile = function(filename) {
-    var that = this;
+    const that = this;
 
     return Promise()
     .then(function() {
-        var filepath = that.resolve(filename);
-        var stat = that.get('fsStatFile');
+        const filepath = that.resolve(filename);
+        const stat = that.get('fsStatFile');
 
         return stat(filepath);
     })
@@ -160,19 +153,19 @@ FS.prototype.statFile = function(filename) {
 };
 
 /**
-    List files/directories in a directory.
-    Directories ends with '/'
+ * List files/directories in a directory.
+ * Directories ends with '/'
 
-    @param {String} dirname
-    @return {Promise<List<String>>}
-*/
+ * @param {String} dirname
+ * @return {Promise<List<String>>}
+ */
 FS.prototype.readDir = function(dirname) {
-    var that = this;
+    const that = this;
 
     return Promise()
     .then(function() {
-        var dirpath = that.resolve(dirname);
-        var readDir = that.get('fsReadDir');
+        const dirpath = that.resolve(dirname);
+        const readDir = that.get('fsReadDir');
 
         return readDir(dirpath);
     })
@@ -182,12 +175,12 @@ FS.prototype.readDir = function(dirname) {
 };
 
 /**
-    List only files in a diretcory
-    Directories ends with '/'
-
-    @param {String} dirname
-    @return {Promise<List<String>>}
-*/
+ * List only files in a diretcory
+ * Directories ends with '/'
+ *
+ * @param {String} dirname
+ * @return {Promise<List<String>>}
+ */
 FS.prototype.listFiles = function(dirname) {
     return this.readDir(dirname)
     .then(function(files) {
@@ -196,21 +189,21 @@ FS.prototype.listFiles = function(dirname) {
 };
 
 /**
-    List all files in a directory
-
-    @param {String} dirName
-    @param {Function(dirName)} filterFn: call it for each file/directory to test if it should stop iterating
-    @return {Promise<List<String>>}
-*/
+ * List all files in a directory
+ *
+ * @param {String} dirName
+ * @param {Function(dirName)} filterFn: call it for each file/directory to test if it should stop iterating
+ * @return {Promise<List<String>>}
+ */
 FS.prototype.listAllFiles = function(dirName, filterFn) {
-    var that = this;
+    const that = this;
     dirName = dirName || '.';
 
     return this.readDir(dirName)
     .then(function(files) {
         return Promise.reduce(files, function(out, file) {
-            var isDirectory = pathIsFolder(file);
-            var newDirName = path.join(dirName, file);
+            const isDirectory = pathIsFolder(file);
+            const newDirName = path.join(dirName, file);
 
             if (filterFn && filterFn(newDirName) === false) {
                 return out;
@@ -229,13 +222,13 @@ FS.prototype.listAllFiles = function(dirName, filterFn) {
 };
 
 /**
-    Find a file in a folder (case insensitive)
-    Return the found filename
-
-    @param {String} dirname
-    @param {String} filename
-    @return {Promise<String>}
-*/
+ * Find a file in a folder (case insensitive)
+ * Return the found filename
+ *
+ * @param {String} dirname
+ * @param {String} filename
+ * @return {Promise<String>}
+ */
 FS.prototype.findFile = function(dirname, filename) {
     return this.listFiles(dirname)
     .then(function(files) {
@@ -246,20 +239,20 @@ FS.prototype.findFile = function(dirname, filename) {
 };
 
 /**
-    Load a JSON file
-    By default, fs only supports JSON
-
-    @param {String} filename
-    @return {Promise<Object>}
-*/
+ * Load a JSON file
+ * By default, fs only supports JSON
+ *
+ * @param {String} filename
+ * @return {Promise<Object>}
+ */
 FS.prototype.loadAsObject = function(filename) {
-    var that = this;
-    var fsLoadObject = this.get('fsLoadObject');
+    const that = this;
+    const fsLoadObject = this.get('fsLoadObject');
 
     return this.exists(filename)
     .then(function(exists) {
         if (!exists) {
-            var err = new Error('Module doesn\'t exist');
+            const err = new Error('Module doesn\'t exist');
             err.code = 'MODULE_NOT_FOUND';
 
             throw err;
@@ -277,22 +270,22 @@ FS.prototype.loadAsObject = function(filename) {
 };
 
 /**
-    Create a FS instance
-
-    @param {Object} def
-    @return {FS}
-*/
+ * Create a FS instance
+ *
+ * @param {Object} def
+ * @return {FS}
+ */
 FS.create = function create(def) {
     return new FS(def);
 };
 
 /**
-    Create a new FS instance with a reduced scope
-
-    @param {FS} fs
-    @param {String} scope
-    @return {FS}
-*/
+ * Create a new FS instance with a reduced scope
+ *
+ * @param {FS} fs
+ * @param {String} scope
+ * @return {FS}
+ */
 FS.reduceScope = function reduceScope(fs, scope) {
     return fs.set('root', path.join(fs.getRoot(), scope));
 };
@@ -300,8 +293,8 @@ FS.reduceScope = function reduceScope(fs, scope) {
 
 // .readdir return files/folder as a list of string, folder ending with '/'
 function pathIsFolder(filename) {
-    var lastChar = filename[filename.length - 1];
+    const lastChar = filename[filename.length - 1];
     return lastChar == '/' || lastChar == '\\';
 }
 
-module.exports = FS;
\ No newline at end of file
+module.exports = FS;
diff --git a/packages/gitbook/lib/models/glossary.js b/packages/gitbook/src/models/glossary.js
index 0033248..e269b14 100644
--- a/packages/gitbook/lib/models/glossary.js
+++ b/packages/gitbook/src/models/glossary.js
@@ -1,11 +1,11 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var error = require('../utils/error');
-var File = require('./file');
-var GlossaryEntry = require('./glossaryEntry');
-var parsers = require('../parsers');
+const error = require('../utils/error');
+const File = require('./file');
+const GlossaryEntry = require('./glossaryEntry');
+const parsers = require('../parsers');
 
-var Glossary = Immutable.Record({
+const Glossary = Immutable.Record({
     file:       File(),
     entries:    Immutable.OrderedMap()
 });
@@ -25,8 +25,8 @@ Glossary.prototype.getEntries = function() {
     @return {GlossaryEntry}
 */
 Glossary.prototype.getEntry = function(name) {
-    var entries = this.getEntries();
-    var id = GlossaryEntry.nameToID(name);
+    const entries = this.getEntries();
+    const id = GlossaryEntry.nameToID(name);
 
     return entries.get(id);
 };
@@ -37,10 +37,10 @@ Glossary.prototype.getEntry = function(name) {
     @return {Promise<String>}
 */
 Glossary.prototype.toText = function(parser) {
-    var file = this.getFile();
-    var entries = this.getEntries();
+    const file = this.getFile();
+    const entries = this.getEntries();
 
-    parser = parser? parsers.getByExt(parser) : file.getParser();
+    parser = parser ? parsers.getByExt(parser) : file.getParser();
 
     if (!parser) {
         throw error.FileNotParsableError({
@@ -60,8 +60,8 @@ Glossary.prototype.toText = function(parser) {
     @return {Glossary}
 */
 Glossary.addEntry = function addEntry(glossary, entry) {
-    var id = entry.getID();
-    var entries = glossary.getEntries();
+    const id = entry.getID();
+    let entries = glossary.getEntries();
 
     entries = entries.set(id, entry);
     return glossary.set('entries', entries);
@@ -75,9 +75,9 @@ Glossary.addEntry = function addEntry(glossary, entry) {
     @return {Glossary}
 */
 Glossary.addEntryByName = function addEntryByName(glossary, name, description) {
-    var entry = new GlossaryEntry({
-        name: name,
-        description: description
+    const entry = new GlossaryEntry({
+        name,
+        description
     });
 
     return Glossary.addEntry(glossary, entry);
@@ -100,7 +100,7 @@ Glossary.createFromEntries = function createFromEntries(file, entries) {
     });
 
     return new Glossary({
-        file: file,
+        file,
         entries: Immutable.OrderedMap(entries)
     });
 };
diff --git a/packages/gitbook/lib/models/glossaryEntry.js b/packages/gitbook/src/models/glossaryEntry.js
index 10791db..b36b276 100644
--- a/packages/gitbook/lib/models/glossaryEntry.js
+++ b/packages/gitbook/src/models/glossaryEntry.js
@@ -1,11 +1,11 @@
-var Immutable = require('immutable');
-var slug = require('github-slugid');
+const Immutable = require('immutable');
+const slug = require('github-slugid');
 
 /*
     A definition represents an entry in the glossary
 */
 
-var GlossaryEntry = Immutable.Record({
+const GlossaryEntry = Immutable.Record({
     name:               String(),
     description:        String()
 });
diff --git a/packages/gitbook/lib/models/ignore.js b/packages/gitbook/src/models/ignore.js
index 499195e..99ade9a 100644
--- a/packages/gitbook/lib/models/ignore.js
+++ b/packages/gitbook/src/models/ignore.js
@@ -1,10 +1,10 @@
-var Immutable = require('immutable');
-var IgnoreMutable = require('ignore');
+const Immutable = require('immutable');
+const IgnoreMutable = require('ignore');
 
 /*
     Immutable version of node-ignore
 */
-var Ignore = Immutable.Record({
+const Ignore = Immutable.Record({
     ignore: new IgnoreMutable()
 }, 'Ignore');
 
@@ -19,7 +19,7 @@ Ignore.prototype.getIgnore = function() {
     @return {Boolean}
 */
 Ignore.prototype.isFileIgnored = function(filename) {
-    var ignore = this.getIgnore();
+    const ignore = this.getIgnore();
     return ignore.filter([filename]).length == 0;
 };
 
@@ -30,8 +30,8 @@ Ignore.prototype.isFileIgnored = function(filename) {
     @return {Ignore}
 */
 Ignore.prototype.add = function(rule) {
-    var ignore = this.getIgnore();
-    var newIgnore = new IgnoreMutable();
+    const ignore = this.getIgnore();
+    const newIgnore = new IgnoreMutable();
 
     newIgnore.add(ignore);
     newIgnore.add(rule);
diff --git a/packages/gitbook/lib/models/language.js b/packages/gitbook/src/models/language.js
index dcefbf6..1413091 100644
--- a/packages/gitbook/lib/models/language.js
+++ b/packages/gitbook/src/models/language.js
@@ -1,7 +1,7 @@
-var path = require('path');
-var Immutable = require('immutable');
+const path = require('path');
+const Immutable = require('immutable');
 
-var Language = Immutable.Record({
+const Language = Immutable.Record({
     title:      String(),
     path:       String()
 });
diff --git a/packages/gitbook/lib/models/languages.js b/packages/gitbook/src/models/languages.js
index 42f05f9..9540546 100644
--- a/packages/gitbook/lib/models/languages.js
+++ b/packages/gitbook/src/models/languages.js
@@ -1,9 +1,9 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var File = require('./file');
-var Language = require('./language');
+const File = require('./file');
+const Language = require('./language');
 
-var Languages = Immutable.Record({
+const Languages = Immutable.Record({
     file:       File(),
     list:       Immutable.OrderedMap()
 });
@@ -52,7 +52,7 @@ Languages.prototype.getCount = function() {
     @return {Language}
 */
 Languages.createFromList = function(file, langs) {
-    var list = Immutable.OrderedMap();
+    let list = Immutable.OrderedMap();
 
     langs.forEach(function(lang) {
         lang = Language({
@@ -63,8 +63,8 @@ Languages.createFromList = function(file, langs) {
     });
 
     return Languages({
-        file: file,
-        list: list
+        file,
+        list
     });
 };
 
diff --git a/packages/gitbook/lib/models/output.js b/packages/gitbook/src/models/output.js
index 0f008ec..55d83a4 100644
--- a/packages/gitbook/lib/models/output.js
+++ b/packages/gitbook/src/models/output.js
@@ -1,9 +1,9 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var Book = require('./book');
-var LocationUtils = require('../utils/location');
+const Book = require('./book');
+const LocationUtils = require('../utils/location');
 
-var Output = Immutable.Record({
+const Output = Immutable.Record({
     book:       Book(),
 
     // Name of the generator being used
@@ -62,7 +62,7 @@ Output.prototype.getState = function() {
 Output.prototype.getPage = function(filePath) {
     filePath = LocationUtils.normalize(filePath);
 
-    var pages = this.getPages();
+    const pages = this.getPages();
     return pages.get(filePath);
 };
 
diff --git a/packages/gitbook/lib/models/page.js b/packages/gitbook/src/models/page.js
index 275a034..dd60298 100644
--- a/packages/gitbook/lib/models/page.js
+++ b/packages/gitbook/src/models/page.js
@@ -1,9 +1,9 @@
-var Immutable = require('immutable');
-var yaml = require('js-yaml');
+const Immutable = require('immutable');
+const yaml = require('js-yaml');
 
-var File = require('./file');
+const File = require('./file');
 
-var Page = Immutable.Record({
+const Page = Immutable.Record({
     file:           File(),
 
     // Attributes extracted from the YAML header
@@ -37,14 +37,14 @@ Page.prototype.getDir = function() {
  * @return {String}
 */
 Page.prototype.toText = function() {
-    var attrs = this.getAttributes();
-    var content = this.getContent();
+    const attrs = this.getAttributes();
+    const content = this.getContent();
 
     if (attrs.size === 0) {
         return content;
     }
 
-    var frontMatter = '---\n' + yaml.safeDump(attrs.toJS(), { skipInvalid: true }) + '---\n\n';
+    const frontMatter = '---\n' + yaml.safeDump(attrs.toJS(), { skipInvalid: true }) + '---\n\n';
     return (frontMatter + content);
 };
 
@@ -63,7 +63,7 @@ Page.prototype.getPath = function() {
 */
 Page.createForFile = function(file) {
     return new Page({
-        file: file
+        file
     });
 };
 
diff --git a/packages/gitbook/lib/models/parser.js b/packages/gitbook/src/models/parser.js
index d64542f..3769dd3 100644
--- a/packages/gitbook/lib/models/parser.js
+++ b/packages/gitbook/src/models/parser.js
@@ -1,7 +1,7 @@
-var Immutable = require('immutable');
-var Promise = require('../utils/promise');
+const Immutable = require('immutable');
+const Promise = require('../utils/promise');
 
-var Parser = Immutable.Record({
+const Parser = Immutable.Record({
     name:           String(),
 
     // List of extensions that can be processed using this parser
@@ -27,22 +27,22 @@ Parser.prototype.getExtensions = function() {
 // PARSE
 
 Parser.prototype.parseReadme = function(content) {
-    var readme = this.get('readme');
+    const readme = this.get('readme');
     return Promise(readme(content));
 };
 
 Parser.prototype.parseSummary = function(content) {
-    var summary = this.get('summary');
+    const summary = this.get('summary');
     return Promise(summary(content));
 };
 
 Parser.prototype.parseGlossary = function(content) {
-    var glossary = this.get('glossary');
+    const glossary = this.get('glossary');
     return Promise(glossary(content));
 };
 
 Parser.prototype.preparePage = function(content) {
-    var page = this.get('page');
+    const page = this.get('page');
     if (!page.prepare) {
         return Promise(content);
     }
@@ -51,39 +51,39 @@ Parser.prototype.preparePage = function(content) {
 };
 
 Parser.prototype.parsePage = function(content) {
-    var page = this.get('page');
+    const page = this.get('page');
     return Promise(page(content));
 };
 
 Parser.prototype.parseInline = function(content) {
-    var inline = this.get('inline');
+    const inline = this.get('inline');
     return Promise(inline(content));
 };
 
 Parser.prototype.parseLanguages = function(content) {
-    var langs = this.get('langs');
+    const langs = this.get('langs');
     return Promise(langs(content));
 };
 
 Parser.prototype.parseInline = function(content) {
-    var inline = this.get('inline');
+    const inline = this.get('inline');
     return Promise(inline(content));
 };
 
 // TO TEXT
 
 Parser.prototype.renderLanguages = function(content) {
-    var langs = this.get('langs');
+    const langs = this.get('langs');
     return Promise(langs.toText(content));
 };
 
 Parser.prototype.renderSummary = function(content) {
-    var summary = this.get('summary');
+    const summary = this.get('summary');
     return Promise(summary.toText(content));
 };
 
 Parser.prototype.renderGlossary = function(content) {
-    var glossary = this.get('glossary');
+    const glossary = this.get('glossary');
     return Promise(glossary.toText(content));
 };
 
@@ -94,7 +94,7 @@ Parser.prototype.renderGlossary = function(content) {
     @return {Boolean}
 */
 Parser.prototype.matchExtension = function(ext) {
-    var exts = this.getExtensions();
+    const exts = this.getExtensions();
     return exts.includes(ext.toLowerCase());
 };
 
@@ -108,7 +108,7 @@ Parser.prototype.matchExtension = function(ext) {
 */
 Parser.create = function(name, extensions, module) {
     return new Parser({
-        name: name,
+        name,
         extensions: Immutable.List(extensions),
         readme:         module.readme,
         langs:          module.langs,
diff --git a/packages/gitbook/lib/models/plugin.js b/packages/gitbook/src/models/plugin.js
index acabba9..0e4c774 100644
--- a/packages/gitbook/lib/models/plugin.js
+++ b/packages/gitbook/src/models/plugin.js
@@ -1,12 +1,12 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var TemplateBlock = require('./templateBlock');
-var PluginDependency = require('./pluginDependency');
-var THEME_PREFIX = require('../constants/themePrefix');
+const TemplateBlock = require('./templateBlock');
+const PluginDependency = require('./pluginDependency');
+const THEME_PREFIX = require('../constants/themePrefix');
 
-var DEFAULT_VERSION = '*';
+const DEFAULT_VERSION = '*';
 
-var Plugin = Immutable.Record({
+const Plugin = Immutable.Record({
     name:       String(),
 
     // Requirement version (ex: ">1.0.0")
@@ -77,7 +77,7 @@ Plugin.prototype.isLoaded = function() {
  * @return {Boolean}
  */
 Plugin.prototype.isTheme = function() {
-    var name = this.getName();
+    const name = this.getName();
     return (name && name.indexOf(THEME_PREFIX) === 0);
 };
 
@@ -99,9 +99,9 @@ Plugin.prototype.getResources = function(type) {
         throw new Error('Invalid assets type ' + type);
     }
 
-    var content = this.getContent();
+    const content = this.getContent();
     return (content.get(type)
-        || (type == 'website'? content.get('book') : null)
+        || (type == 'website' ? content.get('book') : null)
         || Immutable.Map());
 };
 
@@ -118,7 +118,7 @@ Plugin.prototype.getFilters = function() {
  * @return {Map<String:TemplateBlock>}
  */
 Plugin.prototype.getBlocks = function() {
-    var blocks = this.getContent().get('blocks');
+    let blocks = this.getContent().get('blocks');
     blocks = blocks || Immutable.Map();
 
     return blocks
@@ -142,12 +142,12 @@ Plugin.prototype.getHook = function(name) {
  * @return {Plugin}
  */
 Plugin.createFromString = function(s) {
-    var parts = s.split('@');
-    var name = parts[0];
-    var version = parts.slice(1).join('@');
+    const parts = s.split('@');
+    const name = parts[0];
+    const version = parts.slice(1).join('@');
 
     return new Plugin({
-        name: name,
+        name,
         version: version || DEFAULT_VERSION
     });
 };
diff --git a/packages/gitbook/lib/models/pluginDependency.js b/packages/gitbook/src/models/pluginDependency.js
index 8866294..4e5d464 100644
--- a/packages/gitbook/lib/models/pluginDependency.js
+++ b/packages/gitbook/src/models/pluginDependency.js
@@ -1,15 +1,15 @@
-var is = require('is');
-var semver = require('semver');
-var Immutable = require('immutable');
+const is = require('is');
+const semver = require('semver');
+const Immutable = require('immutable');
 
-var PREFIX = require('../constants/pluginPrefix');
-var DEFAULT_VERSION = '*';
+const PREFIX = require('../constants/pluginPrefix');
+const DEFAULT_VERSION = '*';
 
 /*
  * PluginDependency represents the informations about a plugin
  * stored in config.plugins
  */
-var PluginDependency = Immutable.Record({
+const PluginDependency = Immutable.Record({
     name:       String(),
 
     // Requirement version (ex: ">1.0.0")
@@ -71,7 +71,7 @@ PluginDependency.create = function(name, version, enabled) {
     }
 
     return new PluginDependency({
-        name: name,
+        name,
         version: version || DEFAULT_VERSION,
         enabled: Boolean(enabled)
     });
@@ -83,10 +83,10 @@ PluginDependency.create = function(name, version, enabled) {
  * @return {Plugin|undefined}
  */
 PluginDependency.createFromString = function(s) {
-    var parts = s.split('@');
-    var name = parts[0];
-    var version = parts.slice(1).join('@');
-    var enabled = true;
+    const parts = s.split('@');
+    let name = parts[0];
+    const version = parts.slice(1).join('@');
+    let enabled = true;
 
     if (name[0] === '-') {
         enabled = false;
@@ -94,9 +94,9 @@ PluginDependency.createFromString = function(s) {
     }
 
     return new PluginDependency({
-        name: name,
+        name,
         version: version || DEFAULT_VERSION,
-        enabled: enabled
+        enabled
     });
 };
 
@@ -106,7 +106,7 @@ PluginDependency.createFromString = function(s) {
  * @return {List<PluginDependency>}
  */
 PluginDependency.listFromString = function(s) {
-    var parts = s.split(',');
+    const parts = s.split(',');
     return PluginDependency.listFromArray(parts);
 };
 
@@ -140,7 +140,7 @@ PluginDependency.listFromArray = function(arr) {
 PluginDependency.listToArray = function(list) {
     return list
         .map(function(dep) {
-            var result = '';
+            let result = '';
 
             if (!dep.isEnabled()) {
                 result += '-';
diff --git a/packages/gitbook/lib/models/readme.js b/packages/gitbook/src/models/readme.js
index c655c82..0fb52b4 100644
--- a/packages/gitbook/lib/models/readme.js
+++ b/packages/gitbook/src/models/readme.js
@@ -1,8 +1,8 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var File = require('./file');
+const File = require('./file');
 
-var Readme = Immutable.Record({
+const Readme = Immutable.Record({
     file:           File(),
     title:          String(),
     description:    String()
@@ -31,7 +31,7 @@ Readme.create = function(file, def) {
     def = def || {};
 
     return new Readme({
-        file: file,
+        file,
         title: def.title || '',
         description: def.description || ''
     });
diff --git a/packages/gitbook/lib/models/summary.js b/packages/gitbook/src/models/summary.js
index 70f0535..edc202e 100644
--- a/packages/gitbook/lib/models/summary.js
+++ b/packages/gitbook/src/models/summary.js
@@ -1,14 +1,14 @@
-var is = require('is');
-var Immutable = require('immutable');
+const is = require('is');
+const Immutable = require('immutable');
 
-var error = require('../utils/error');
-var LocationUtils = require('../utils/location');
-var File = require('./file');
-var SummaryPart = require('./summaryPart');
-var SummaryArticle = require('./summaryArticle');
-var parsers = require('../parsers');
+const error = require('../utils/error');
+const LocationUtils = require('../utils/location');
+const File = require('./file');
+const SummaryPart = require('./summaryPart');
+const SummaryArticle = require('./summaryArticle');
+const parsers = require('../parsers');
 
-var Summary = Immutable.Record({
+const Summary = Immutable.Record({
     file:       File(),
     parts:      Immutable.List()
 }, 'Summary');
@@ -28,7 +28,7 @@ Summary.prototype.getParts = function() {
     @return {Part}
 */
 Summary.prototype.getPart = function(i) {
-    var parts = this.getParts();
+    const parts = this.getParts();
     return parts.get(i);
 };
 
@@ -41,7 +41,7 @@ Summary.prototype.getPart = function(i) {
     @return {Article|Part}
 */
 Summary.prototype.getArticle = function(iter, partIter) {
-    var parts = this.getParts();
+    const parts = this.getParts();
 
     return parts.reduce(function(result, part) {
         if (result) return result;
@@ -74,7 +74,7 @@ Summary.prototype.getByLevel = function(level) {
 */
 Summary.prototype.getByPath = function(filePath) {
     return this.getArticle(function(article) {
-        var articlePath = article.getPath();
+        const articlePath = article.getPath();
 
         return (
             articlePath &&
@@ -101,8 +101,8 @@ Summary.prototype.getFirstArticle = function() {
     @return {Article}
 */
 Summary.prototype.getNextArticle = function(current) {
-    var level = is.string(current)? current : current.getLevel();
-    var wasPrev = false;
+    const level = is.string(current) ? current : current.getLevel();
+    let wasPrev = false;
 
     return this.getArticle(function(article) {
         if (wasPrev) return true;
@@ -119,8 +119,8 @@ Summary.prototype.getNextArticle = function(current) {
     @return {Article}
 */
 Summary.prototype.getPrevArticle = function(current) {
-    var level = is.string(current)? current : current.getLevel();
-    var prev = undefined;
+    const level = is.string(current) ? current : current.getLevel();
+    let prev = undefined;
 
     this.getArticle(function(article) {
         if (article.getLevel() == level) {
@@ -140,18 +140,18 @@ Summary.prototype.getPrevArticle = function(current) {
     @param {String|Article} current
     @return {Article|Part|Null}
 */
-Summary.prototype.getParent = function (level) {
+Summary.prototype.getParent = function(level) {
     // Coerce to level
-    level = is.string(level)? level : level.getLevel();
+    level = is.string(level) ? level : level.getLevel();
 
     // Get parent level
-    var parentLevel = getParentLevel(level);
+    const parentLevel = getParentLevel(level);
     if (!parentLevel) {
         return null;
     }
 
     // Get parent of the position
-    var parentArticle = this.getByLevel(parentLevel);
+    const parentArticle = this.getByLevel(parentLevel);
     return parentArticle || null;
 };
 
@@ -162,10 +162,10 @@ Summary.prototype.getParent = function (level) {
     @return {Promise<String>}
 */
 Summary.prototype.toText = function(parseExt) {
-    var file = this.getFile();
-    var parts = this.getParts();
+    const file = this.getFile();
+    const parts = this.getParts();
 
-    var parser = parseExt? parsers.getByExt(parseExt) : file.getParser();
+    const parser = parseExt ? parsers.getByExt(parseExt) : file.getParser();
 
     if (!parser) {
         throw error.FileNotParsableError({
@@ -184,7 +184,7 @@ Summary.prototype.toText = function(parseExt) {
     @return {List<Article>}
 */
 Summary.prototype.getArticlesAsList = function() {
-    var accu = [];
+    const accu = [];
 
     this.getArticle(function(article) {
         accu.push(article);
@@ -209,7 +209,7 @@ Summary.createFromParts = function createFromParts(file, parts) {
     });
 
     return new Summary({
-        file: file,
+        file,
         parts: new Immutable.List(parts)
     });
 };
@@ -221,7 +221,7 @@ Summary.createFromParts = function createFromParts(file, parts) {
     @return {String}
 */
 function getParentLevel(level) {
-    var parts = level.split('.');
+    const parts = level.split('.');
     return parts.slice(0, -1).join('.');
 }
 
diff --git a/packages/gitbook/lib/models/summaryArticle.js b/packages/gitbook/src/models/summaryArticle.js
index 6da8d1d..919e6b9 100644
--- a/packages/gitbook/lib/models/summaryArticle.js
+++ b/packages/gitbook/src/models/summaryArticle.js
@@ -1,12 +1,12 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var location = require('../utils/location');
+const location = require('../utils/location');
 
 /*
     An article represents an entry in the Summary / table of Contents
 */
 
-var SummaryArticle = Immutable.Record({
+const SummaryArticle = Immutable.Record({
     level:      String(),
     title:      String(),
     ref:        String(),
@@ -50,14 +50,14 @@ SummaryArticle.prototype.getPath = function() {
         return undefined;
     }
 
-    var ref = this.getRef();
+    const ref = this.getRef();
     if (!ref) {
         return undefined;
     }
 
-    var parts = ref.split('#');
+    const parts = ref.split('#');
 
-    var pathname = (parts.length > 1? parts.slice(0, -1).join('#') : ref);
+    const pathname = (parts.length > 1 ? parts.slice(0, -1).join('#') : ref);
 
     // Normalize path to remove ('./', '/...', etc)
     return location.flatten(pathname);
@@ -69,7 +69,7 @@ SummaryArticle.prototype.getPath = function() {
  * @return {String}
  */
 SummaryArticle.prototype.getUrl = function() {
-    return this.isExternal()? this.getRef() : undefined;
+    return this.isExternal() ? this.getRef() : undefined;
 };
 
 /**
@@ -78,10 +78,10 @@ SummaryArticle.prototype.getUrl = function() {
  * @return {String}
  */
 SummaryArticle.prototype.getAnchor = function() {
-    var ref = this.getRef();
-    var parts = ref.split('#');
+    const ref = this.getRef();
+    const parts = ref.split('#');
 
-    var anchor = (parts.length > 1? '#' + parts[parts.length - 1] : undefined);
+    const anchor = (parts.length > 1 ? '#' + parts[parts.length - 1] : undefined);
     return anchor;
 };
 
@@ -91,9 +91,9 @@ SummaryArticle.prototype.getAnchor = function() {
  * @return {String}
  */
 SummaryArticle.prototype.createChildLevel = function() {
-    var level       = this.getLevel();
-    var subArticles = this.getArticles();
-    var childLevel  = level + '.' + (subArticles.size + 1);
+    const level       = this.getLevel();
+    const subArticles = this.getArticles();
+    const childLevel  = level + '.' + (subArticles.size + 1);
 
     return childLevel;
 };
@@ -127,8 +127,8 @@ SummaryArticle.prototype.isFile = function(file) {
  * @return {Boolean}
  */
 SummaryArticle.prototype.isReadme = function(book) {
-    var readme = book.getFile? book : book.getReadme();
-    var file = readme.getFile();
+    const readme = book.getFile ? book : book.getReadme();
+    const file = readme.getFile();
 
     return this.isFile(file);
 };
@@ -149,7 +149,7 @@ SummaryArticle.prototype.isExternal = function() {
  * @return {SummaryArticle}
  */
 SummaryArticle.create = function(def, level) {
-    var articles = (def.articles || []).map(function(article, i) {
+    const articles = (def.articles || []).map(function(article, i) {
         if (article instanceof SummaryArticle) {
             return article;
         }
@@ -157,7 +157,7 @@ SummaryArticle.create = function(def, level) {
     });
 
     return new SummaryArticle({
-        level: level,
+        level,
         title: def.title,
         ref: def.ref || def.path || '',
         articles: Immutable.List(articles)
@@ -172,7 +172,7 @@ SummaryArticle.create = function(def, level) {
  * @return {Article}
  */
 SummaryArticle.findArticle = function(base, iter) {
-    var articles = base.getArticles();
+    const articles = base.getArticles();
 
     return articles.reduce(function(result, article) {
         if (result) return result;
diff --git a/packages/gitbook/lib/models/summaryPart.js b/packages/gitbook/src/models/summaryPart.js
index f0e6f57..0bb5369 100644
--- a/packages/gitbook/lib/models/summaryPart.js
+++ b/packages/gitbook/src/models/summaryPart.js
@@ -1,12 +1,12 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var SummaryArticle = require('./summaryArticle');
+const SummaryArticle = require('./summaryArticle');
 
 /*
     A part represents a section in the Summary / table of Contents
 */
 
-var SummaryPart = Immutable.Record({
+const SummaryPart = Immutable.Record({
     level:      String(),
     title:      String(),
     articles:   Immutable.List()
@@ -30,9 +30,9 @@ SummaryPart.prototype.getArticles = function() {
  * @return {String}
  */
 SummaryPart.prototype.createChildLevel = function() {
-    var level       = this.getLevel();
-    var subArticles = this.getArticles();
-    var childLevel  = level + '.' + (subArticles.size + 1);
+    const level       = this.getLevel();
+    const subArticles = this.getArticles();
+    const childLevel  = level + '.' + (subArticles.size + 1);
 
     return childLevel;
 };
@@ -44,7 +44,7 @@ SummaryPart.prototype.createChildLevel = function() {
  * @return {SummaryPart}
  */
 SummaryPart.create = function(def, level) {
-    var articles = (def.articles || []).map(function(article, i) {
+    const articles = (def.articles || []).map(function(article, i) {
         if (article instanceof SummaryArticle) {
             return article;
         }
diff --git a/packages/gitbook/lib/models/templateBlock.js b/packages/gitbook/src/models/templateBlock.js
index 458f084..a0b9aaa 100644
--- a/packages/gitbook/lib/models/templateBlock.js
+++ b/packages/gitbook/src/models/templateBlock.js
@@ -1,14 +1,14 @@
-var is = require('is');
-var extend = require('extend');
-var Immutable = require('immutable');
+const is = require('is');
+const extend = require('extend');
+const Immutable = require('immutable');
 
-var Promise = require('../utils/promise');
-var genKey = require('../utils/genKey');
-var TemplateShortcut = require('./templateShortcut');
+const Promise = require('../utils/promise');
+const genKey = require('../utils/genKey');
+const TemplateShortcut = require('./templateShortcut');
 
-var NODE_ENDARGS = '%%endargs%%';
+const NODE_ENDARGS = '%%endargs%%';
 
-var TemplateBlock = Immutable.Record({
+const TemplateBlock = Immutable.Record({
     // Name of block, also the start tag
     name:           String(),
 
@@ -47,7 +47,7 @@ TemplateBlock.prototype.getBlocks = function() {
  * @return {TemplateShortcut|undefined}
  */
 TemplateBlock.prototype.getShortcuts = function() {
-    var shortcuts = this.get('shortcuts');
+    const shortcuts = this.get('shortcuts');
     if (shortcuts.size === 0) {
         return undefined;
     }
@@ -70,33 +70,33 @@ TemplateBlock.prototype.getExtensionName = function() {
 TemplateBlock.prototype.toNunjucksExt = function(mainContext, blocksOutput) {
     blocksOutput = blocksOutput || {};
 
-    var that = this;
-    var name = this.getName();
-    var endTag = this.getEndTag();
-    var blocks = this.getBlocks().toJS();
+    const that = this;
+    const name = this.getName();
+    const endTag = this.getEndTag();
+    const blocks = this.getBlocks().toJS();
 
     function Ext() {
         this.tags = [name];
 
         this.parse = function(parser, nodes) {
-            var lastBlockName = null;
-            var lastBlockArgs = null;
-            var allBlocks = blocks.concat([endTag]);
+            let lastBlockName = null;
+            let lastBlockArgs = null;
+            const allBlocks = blocks.concat([endTag]);
 
             // Parse first block
-            var tok = parser.nextToken();
+            const tok = parser.nextToken();
             lastBlockArgs = parser.parseSignature(null, true);
             parser.advanceAfterBlockEnd(tok.value);
 
-            var args = new nodes.NodeList();
-            var bodies = [];
-            var blockNamesNode = new nodes.Array(tok.lineno, tok.colno);
-            var blockArgCounts = new nodes.Array(tok.lineno, tok.colno);
+            const args = new nodes.NodeList();
+            const bodies = [];
+            const blockNamesNode = new nodes.Array(tok.lineno, tok.colno);
+            const blockArgCounts = new nodes.Array(tok.lineno, tok.colno);
 
             // Parse while we found "end<block>"
             do {
                 // Read body
-                var currentBody = parser.parseUntilBlocks.apply(parser, allBlocks);
+                const currentBody = parser.parseUntilBlocks(...allBlocks);
 
                 // Handle body with previous block name and args
                 blockNamesNode.addChild(new nodes.Literal(args.lineno, args.colno, lastBlockName));
@@ -126,53 +126,48 @@ TemplateBlock.prototype.toNunjucksExt = function(mainContext, blocksOutput) {
             return new nodes.CallExtensionAsync(this, 'run', args, bodies);
         };
 
-        this.run = function(context) {
-            var fnArgs = Array.prototype.slice.call(arguments, 1);
-
-            var args;
-            var blocks = [];
-            var bodies = [];
-            var blockNames;
-            var blockArgCounts;
-            var callback;
+        this.run = function(context, ...fnArgs) {
+            let args;
+            const blocks = [];
+            let bodies = [];
 
             // Extract callback
-            callback = fnArgs.pop();
+            const callback = fnArgs.pop();
 
             // Detect end of arguments
-            var endArgIndex = fnArgs.indexOf(NODE_ENDARGS);
+            const endArgIndex = fnArgs.indexOf(NODE_ENDARGS);
 
             // Extract arguments and bodies
             args = fnArgs.slice(0, endArgIndex);
             bodies = fnArgs.slice(endArgIndex + 1);
 
             // Extract block counts
-            blockArgCounts = args.pop();
-            blockNames = args.pop();
+            const blockArgCounts = args.pop();
+            const blockNames = args.pop();
 
             // Recreate list of blocks
-            blockNames.forEach(function(name, i) {
-                var countArgs = blockArgCounts[i];
-                var blockBody = bodies.shift();
+            blockNames.forEach((blkName, i) => {
+                const countArgs = blockArgCounts[i];
+                const blockBody = bodies.shift();
 
-                var blockArgs = countArgs > 0? args.slice(0, countArgs) : [];
+                const blockArgs = countArgs > 0 ? args.slice(0, countArgs) : [];
                 args = args.slice(countArgs);
-                var blockKwargs = extractKwargs(blockArgs);
+                const blockKwargs = extractKwargs(blockArgs);
 
                 blocks.push({
-                    name: name,
+                    blkName,
                     body: blockBody(),
                     args: blockArgs,
                     kwargs: blockKwargs
                 });
             });
 
-            var mainBlock = blocks.shift();
+            const mainBlock = blocks.shift();
             mainBlock.blocks = blocks;
 
             Promise()
             .then(function() {
-                var ctx = extend({
+                const ctx = extend({
                     ctx: context
                 }, mainContext || {});
 
@@ -195,14 +190,14 @@ TemplateBlock.prototype.toNunjucksExt = function(mainContext, blocksOutput) {
  * @return {Promise<String>|String}
  */
 TemplateBlock.prototype.applyBlock = function(inner, context) {
-    var processFn = this.getProcess();
+    const processFn = this.getProcess();
 
     inner = inner || {};
     inner.args = inner.args || [];
     inner.kwargs = inner.kwargs || {};
     inner.blocks = inner.blocks || [];
 
-    var r = processFn.call(context, inner);
+    const r = processFn.call(context, inner);
 
     if (Promise.isPromiseAlike(r)) {
         return r.then(this.normalizeBlockResult.bind(this));
@@ -232,8 +227,8 @@ TemplateBlock.prototype.normalizeBlockResult = function(result) {
  * @return {String}
  */
 TemplateBlock.prototype.blockResultToHtml = function(result, blocksOutput) {
-    var indexedKey;
-    var toIndex = (!result.parse) || (result.post !== undefined);
+    let indexedKey;
+    const toIndex = (!result.parse) || (result.post !== undefined);
 
     if (toIndex) {
         indexedKey = genKey();
@@ -274,8 +269,8 @@ TemplateBlock.create = function(blockName, block) {
  * @return {Object}
  */
 function extractKwargs(args) {
-    var last = args[args.length - 1];
-    return (is.object(last) && last.__keywords)? args.pop() : {};
+    const last = args[args.length - 1];
+    return (is.object(last) && last.__keywords) ? args.pop() : {};
 }
 
 module.exports = TemplateBlock;
diff --git a/packages/gitbook/lib/models/templateEngine.js b/packages/gitbook/src/models/templateEngine.js
index 5724d55..b218a9d 100644
--- a/packages/gitbook/lib/models/templateEngine.js
+++ b/packages/gitbook/src/models/templateEngine.js
@@ -1,7 +1,7 @@
-var nunjucks = require('nunjucks');
-var Immutable = require('immutable');
+const nunjucks = require('nunjucks');
+const Immutable = require('immutable');
 
-var TemplateEngine = Immutable.Record({
+const TemplateEngine = Immutable.Record({
     // Map of {TemplateBlock}
     blocks:     Immutable.Map(),
 
@@ -56,7 +56,7 @@ TemplateEngine.prototype.getExtensions = function() {
     @return {TemplateBlock}
 */
 TemplateEngine.prototype.getBlock = function(name) {
-    var blocks = this.getBlocks();
+    const blocks = this.getBlocks();
     return blocks.find(function(block) {
         return block.getName() === name;
     });
@@ -68,14 +68,14 @@ TemplateEngine.prototype.getBlock = function(name) {
     @return {Nunjucks.Environment}
 */
 TemplateEngine.prototype.toNunjucks = function(blocksOutput) {
-    var loader = this.getLoader();
-    var blocks = this.getBlocks();
-    var filters = this.getFilters();
-    var globals = this.getGlobals();
-    var extensions = this.getExtensions();
-    var context = this.getContext();
-
-    var env = new nunjucks.Environment(
+    const loader = this.getLoader();
+    const blocks = this.getBlocks();
+    const filters = this.getFilters();
+    const globals = this.getGlobals();
+    const extensions = this.getExtensions();
+    const context = this.getContext();
+
+    const env = new nunjucks.Environment(
         loader,
         {
             // Escaping is done after by the asciidoc/markdown parser
@@ -100,8 +100,8 @@ TemplateEngine.prototype.toNunjucks = function(blocksOutput) {
 
     // Add blocks
     blocks.forEach(function(block) {
-        var extName = block.getExtensionName();
-        var Ext = block.toNunjucksExt(context, blocksOutput);
+        const extName = block.getExtensionName();
+        const Ext = block.toNunjucksExt(context, blocksOutput);
 
         env.addExtension(extName, new Ext());
     });
diff --git a/packages/gitbook/lib/models/templateOutput.js b/packages/gitbook/src/models/templateOutput.js
index ae63c06..c6ff730 100644
--- a/packages/gitbook/lib/models/templateOutput.js
+++ b/packages/gitbook/src/models/templateOutput.js
@@ -1,6 +1,6 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var TemplateOutput = Immutable.Record({
+const TemplateOutput = Immutable.Record({
     // Text content of the template
     content:        String(),
 
@@ -34,7 +34,7 @@ TemplateOutput.prototype.setContent = function(content) {
  */
 TemplateOutput.create = function(content, blocks) {
     return new TemplateOutput({
-        content:    content,
+        content,
         blocks:     Immutable.fromJS(blocks)
     });
 };
diff --git a/packages/gitbook/lib/models/templateShortcut.js b/packages/gitbook/src/models/templateShortcut.js
index 309fa6d..b6e1ed9 100644
--- a/packages/gitbook/lib/models/templateShortcut.js
+++ b/packages/gitbook/src/models/templateShortcut.js
@@ -1,11 +1,11 @@
-var Immutable = require('immutable');
-var is = require('is');
+const Immutable = require('immutable');
+const is = require('is');
 
 /*
     A TemplateShortcut is defined in plugin's template blocks
     to replace content with a templating block using delimiters.
 */
-var TemplateShortcut = Immutable.Record({
+const TemplateShortcut = Immutable.Record({
     // List of parser names accepting this shortcut
     parsers:     Immutable.Map(),
 
@@ -47,7 +47,7 @@ TemplateShortcut.prototype.acceptParser = function(parser) {
         parser = parser.getName();
     }
 
-    var parserNames = this.get('parsers');
+    const parserNames = this.get('parsers');
     return parserNames.includes(parser);
 };
 
diff --git a/packages/gitbook/lib/modifiers/config/__tests__/addPlugin.js b/packages/gitbook/src/modifiers/config/__tests__/addPlugin.js
index 61082c9..65fd8f9 100644
--- a/packages/gitbook/lib/modifiers/config/__tests__/addPlugin.js
+++ b/packages/gitbook/src/modifiers/config/__tests__/addPlugin.js
@@ -1,13 +1,13 @@
-var addPlugin = require('../addPlugin');
-var Config = require('../../../models/config');
+const addPlugin = require('../addPlugin');
+const Config = require('../../../models/config');
 
 describe('addPlugin', function() {
-    var config = Config.createWithValues({
+    const config = Config.createWithValues({
         plugins: ['hello', 'world', '-disabled']
     });
 
     it('should have correct state of dependencies', function() {
-        var disabledDep = config.getPluginDependency('disabled');
+        const disabledDep = config.getPluginDependency('disabled');
 
         expect(disabledDep).toBeDefined();
         expect(disabledDep.getVersion()).toEqual('*');
@@ -15,18 +15,17 @@ describe('addPlugin', function() {
     });
 
     it('should add the plugin to the list', function() {
-        var newConfig = addPlugin(config, 'test');
+        const newConfig = addPlugin(config, 'test');
 
-        var testDep = newConfig.getPluginDependency('test');
+        const testDep = newConfig.getPluginDependency('test');
         expect(testDep).toBeDefined();
         expect(testDep.getVersion()).toEqual('*');
         expect(testDep.isEnabled()).toBeTruthy();
 
-        var disabledDep = newConfig.getPluginDependency('disabled');
+        const disabledDep = newConfig.getPluginDependency('disabled');
         expect(disabledDep).toBeDefined();
         expect(disabledDep.getVersion()).toEqual('*');
         expect(disabledDep.isEnabled()).toBeFalsy();
     });
 });
 
-
diff --git a/packages/gitbook/lib/modifiers/config/__tests__/removePlugin.js b/packages/gitbook/src/modifiers/config/__tests__/removePlugin.js
index 253cc39..5450b30 100644
--- a/packages/gitbook/lib/modifiers/config/__tests__/removePlugin.js
+++ b/packages/gitbook/src/modifiers/config/__tests__/removePlugin.js
@@ -1,33 +1,32 @@
-var removePlugin = require('../removePlugin');
-var Config = require('../../../models/config');
+const removePlugin = require('../removePlugin');
+const Config = require('../../../models/config');
 
 describe('removePlugin', function() {
-    var config = Config.createWithValues({
+    const config = Config.createWithValues({
         plugins: ['hello', 'world', '-disabled']
     });
 
     it('should remove the plugin from the list', function() {
-        var newConfig = removePlugin(config, 'hello');
+        const newConfig = removePlugin(config, 'hello');
 
-        var testDep = newConfig.getPluginDependency('hello');
+        const testDep = newConfig.getPluginDependency('hello');
         expect(testDep).toNotBeDefined();
     });
 
     it('should remove the disabled plugin from the list', function() {
-        var newConfig = removePlugin(config, 'disabled');
+        const newConfig = removePlugin(config, 'disabled');
 
-        var testDep = newConfig.getPluginDependency('disabled');
+        const testDep = newConfig.getPluginDependency('disabled');
         expect(testDep).toNotBeDefined();
     });
 
     it('should disable default plugin', function() {
-        var newConfig = removePlugin(config, 'search');
+        const newConfig = removePlugin(config, 'search');
 
-        var disabledDep = newConfig.getPluginDependency('search');
+        const disabledDep = newConfig.getPluginDependency('search');
         expect(disabledDep).toBeDefined();
         expect(disabledDep.getVersion()).toEqual('*');
         expect(disabledDep.isEnabled()).toBeFalsy();
     });
 });
 
-
diff --git a/packages/gitbook/lib/modifiers/config/__tests__/togglePlugin.js b/packages/gitbook/src/modifiers/config/__tests__/togglePlugin.js
index 4127853..6d23ae0 100644
--- a/packages/gitbook/lib/modifiers/config/__tests__/togglePlugin.js
+++ b/packages/gitbook/src/modifiers/config/__tests__/togglePlugin.js
@@ -1,28 +1,27 @@
-var togglePlugin = require('../togglePlugin');
-var Config = require('../../../models/config');
+const togglePlugin = require('../togglePlugin');
+const Config = require('../../../models/config');
 
 describe('togglePlugin', function() {
-    var config = Config.createWithValues({
+    const config = Config.createWithValues({
         plugins: ['hello', 'world', '-disabled']
     });
 
     it('should enable plugin', function() {
-        var newConfig = togglePlugin(config, 'disabled');
+        const newConfig = togglePlugin(config, 'disabled');
 
-        var testDep = newConfig.getPluginDependency('disabled');
+        const testDep = newConfig.getPluginDependency('disabled');
         expect(testDep).toBeDefined();
         expect(testDep.getVersion()).toEqual('*');
         expect(testDep.isEnabled()).toBeTruthy();
     });
 
     it('should disable plugin', function() {
-        var newConfig = togglePlugin(config, 'world');
+        const newConfig = togglePlugin(config, 'world');
 
-        var testDep = newConfig.getPluginDependency('world');
+        const testDep = newConfig.getPluginDependency('world');
         expect(testDep).toBeDefined();
         expect(testDep.getVersion()).toEqual('*');
         expect(testDep.isEnabled()).toBeFalsy();
     });
 });
 
-
diff --git a/packages/gitbook/lib/modifiers/config/addPlugin.js b/packages/gitbook/src/modifiers/config/addPlugin.js
index b8d4ea1..e9ed259 100644
--- a/packages/gitbook/lib/modifiers/config/addPlugin.js
+++ b/packages/gitbook/src/modifiers/config/addPlugin.js
@@ -1,6 +1,6 @@
-var PluginDependency = require('../../models/pluginDependency');
-var togglePlugin = require('./togglePlugin');
-var isDefaultPlugin = require('./isDefaultPlugin');
+const PluginDependency = require('../../models/pluginDependency');
+const togglePlugin = require('./togglePlugin');
+const isDefaultPlugin = require('./isDefaultPlugin');
 
 /**
  * Add a plugin to a book's configuration
@@ -15,8 +15,8 @@ function addPlugin(config, pluginName, version) {
         return togglePlugin(config, pluginName, true);
     }
 
-    var deps = config.getPluginDependencies();
-    var dep = PluginDependency.create(pluginName, version);
+    let deps = config.getPluginDependencies();
+    const dep = PluginDependency.create(pluginName, version);
 
     deps = deps.push(dep);
     return config.setPluginDependencies(deps);
diff --git a/packages/gitbook/lib/modifiers/config/editPlugin.js b/packages/gitbook/src/modifiers/config/editPlugin.js
index a792acd..dd7fd11 100644
--- a/packages/gitbook/lib/modifiers/config/editPlugin.js
+++ b/packages/gitbook/src/modifiers/config/editPlugin.js
@@ -7,7 +7,7 @@
  * @return {Config}
  */
 function editPlugin(config, pluginName, pluginConfig) {
-    return config.setValue('pluginsConfig.'+pluginName, pluginConfig);
+    return config.setValue('pluginsConfig.' + pluginName, pluginConfig);
 }
 
 module.exports = editPlugin;
diff --git a/packages/gitbook/lib/modifiers/config/getPluginConfig.js b/packages/gitbook/src/modifiers/config/getPluginConfig.js
index ae76de8..ed7d6ea 100644
--- a/packages/gitbook/lib/modifiers/config/getPluginConfig.js
+++ b/packages/gitbook/src/modifiers/config/getPluginConfig.js
@@ -5,11 +5,11 @@
  * @return {Object}
  */
 function getPluginConfig(config, pluginName) {
-    var pluginsConfig = config.getValues().get('pluginsConfig');
+    const pluginsConfig = config.getValues().get('pluginsConfig');
     if (pluginsConfig === undefined) {
         return {};
     }
-    var pluginConf = pluginsConfig.get(pluginName);
+    const pluginConf = pluginsConfig.get(pluginName);
     if (pluginConf === undefined) {
         return {};
     } else {
diff --git a/packages/gitbook/lib/modifiers/config/hasPlugin.js b/packages/gitbook/src/modifiers/config/hasPlugin.js
index 9aab4f2..9aab4f2 100644
--- a/packages/gitbook/lib/modifiers/config/hasPlugin.js
+++ b/packages/gitbook/src/modifiers/config/hasPlugin.js
diff --git a/packages/gitbook/lib/modifiers/config/index.js b/packages/gitbook/src/modifiers/config/index.js
index b3de0b0..b3de0b0 100644
--- a/packages/gitbook/lib/modifiers/config/index.js
+++ b/packages/gitbook/src/modifiers/config/index.js
diff --git a/packages/gitbook/lib/modifiers/config/isDefaultPlugin.js b/packages/gitbook/src/modifiers/config/isDefaultPlugin.js
index 63a141d..096e21a 100644
--- a/packages/gitbook/lib/modifiers/config/isDefaultPlugin.js
+++ b/packages/gitbook/src/modifiers/config/isDefaultPlugin.js
@@ -1,5 +1,5 @@
-var DEFAULT_PLUGINS = require('../../constants/defaultPlugins');
-var hasPlugin = require('./hasPlugin');
+const DEFAULT_PLUGINS = require('../../constants/defaultPlugins');
+const hasPlugin = require('./hasPlugin');
 
 /**
  * Test if a plugin is a default one
diff --git a/packages/gitbook/lib/modifiers/config/removePlugin.js b/packages/gitbook/src/modifiers/config/removePlugin.js
index ec06d1e..c80ab84 100644
--- a/packages/gitbook/lib/modifiers/config/removePlugin.js
+++ b/packages/gitbook/src/modifiers/config/removePlugin.js
@@ -1,5 +1,5 @@
-var togglePlugin = require('./togglePlugin');
-var isDefaultPlugin = require('./isDefaultPlugin');
+const togglePlugin = require('./togglePlugin');
+const isDefaultPlugin = require('./isDefaultPlugin');
 
 /**
  * Remove a plugin from a book's configuration
@@ -8,7 +8,7 @@ var isDefaultPlugin = require('./isDefaultPlugin');
  * @return {Config}
  */
 function removePlugin(config, pluginName) {
-    var deps = config.getPluginDependencies();
+    let deps = config.getPluginDependencies();
 
     // For default plugin, we have to disable it instead of removing from the list
     if (isDefaultPlugin(pluginName)) {
diff --git a/packages/gitbook/lib/modifiers/config/togglePlugin.js b/packages/gitbook/src/modifiers/config/togglePlugin.js
index a49e3b9..12a6dec 100644
--- a/packages/gitbook/lib/modifiers/config/togglePlugin.js
+++ b/packages/gitbook/src/modifiers/config/togglePlugin.js
@@ -1,6 +1,6 @@
-var PluginDependency = require('../../models/pluginDependency');
-var hasPlugin = require('./hasPlugin');
-var isDefaultPlugin = require('./isDefaultPlugin');
+const PluginDependency = require('../../models/pluginDependency');
+const hasPlugin = require('./hasPlugin');
+const isDefaultPlugin = require('./isDefaultPlugin');
 
 /**
  * Enable/disable a plugin dependency
@@ -10,7 +10,7 @@ var isDefaultPlugin = require('./isDefaultPlugin');
  * @return {Config}
  */
 function togglePlugin(config, pluginName, state) {
-    var deps = config.getPluginDependencies();
+    let deps = config.getPluginDependencies();
 
     // For default plugin, we should ensure it's listed first
     if (isDefaultPlugin(pluginName) && !hasPlugin(deps, pluginName)) {
diff --git a/packages/gitbook/lib/modifiers/index.js b/packages/gitbook/src/modifiers/index.js
index ad24604..ad24604 100644
--- a/packages/gitbook/lib/modifiers/index.js
+++ b/packages/gitbook/src/modifiers/index.js
diff --git a/packages/gitbook/lib/modifiers/summary/__tests__/editArticle.js b/packages/gitbook/src/modifiers/summary/__tests__/editArticle.js
index e69de29..e69de29 100644
--- a/packages/gitbook/lib/modifiers/summary/__tests__/editArticle.js
+++ b/packages/gitbook/src/modifiers/summary/__tests__/editArticle.js
diff --git a/packages/gitbook/lib/modifiers/summary/__tests__/editPartTitle.js b/packages/gitbook/src/modifiers/summary/__tests__/editPartTitle.js
index d1b916b..aa14a34 100644
--- a/packages/gitbook/lib/modifiers/summary/__tests__/editPartTitle.js
+++ b/packages/gitbook/src/modifiers/summary/__tests__/editPartTitle.js
@@ -1,9 +1,9 @@
-var Summary = require('../../../models/summary');
-var File = require('../../../models/file');
+const Summary = require('../../../models/summary');
+const File = require('../../../models/file');
 
 describe('editPartTitle', function() {
-    var editPartTitle = require('../editPartTitle');
-    var summary = Summary.createFromParts(File(), [
+    const editPartTitle = require('../editPartTitle');
+    const summary = Summary.createFromParts(File(), [
         {
             articles: [
                 {
@@ -22,23 +22,22 @@ describe('editPartTitle', function() {
     ]);
 
     it('should correctly set title of first part', function() {
-        var newSummary = editPartTitle(summary, 0, 'Hello World');
-        var part = newSummary.getPart(0);
+        const newSummary = editPartTitle(summary, 0, 'Hello World');
+        const part = newSummary.getPart(0);
 
         expect(part.getTitle()).toBe('Hello World');
     });
 
     it('should correctly set title of second part', function() {
-        var newSummary = editPartTitle(summary, 1, 'Hello');
-        var part = newSummary.getPart(1);
+        const newSummary = editPartTitle(summary, 1, 'Hello');
+        const part = newSummary.getPart(1);
 
         expect(part.getTitle()).toBe('Hello');
     });
 
     it('should not fail if part doesn\'t exist', function() {
-        var newSummary = editPartTitle(summary, 3, 'Hello');
+        const newSummary = editPartTitle(summary, 3, 'Hello');
         expect(newSummary.getParts().size).toBe(2);
     });
 });
 
-
diff --git a/packages/gitbook/lib/modifiers/summary/__tests__/insertArticle.js b/packages/gitbook/src/modifiers/summary/__tests__/insertArticle.js
index 1ee1c8a..d5ae9bc 100644
--- a/packages/gitbook/lib/modifiers/summary/__tests__/insertArticle.js
+++ b/packages/gitbook/src/modifiers/summary/__tests__/insertArticle.js
@@ -1,10 +1,10 @@
-var Summary = require('../../../models/summary');
-var SummaryArticle = require('../../../models/summaryArticle');
-var File = require('../../../models/file');
+const Summary = require('../../../models/summary');
+const SummaryArticle = require('../../../models/summaryArticle');
+const File = require('../../../models/file');
 
 describe('insertArticle', function() {
-    var insertArticle = require('../insertArticle');
-    var summary = Summary.createFromParts(File(), [
+    const insertArticle = require('../insertArticle');
+    const summary = Summary.createFromParts(File(), [
         {
             articles: [
                 {
@@ -43,14 +43,14 @@ describe('insertArticle', function() {
     ]);
 
     it('should insert an article at a given level', function() {
-        var article = SummaryArticle.create({
+        const article = SummaryArticle.create({
             title: 'Inserted'
         }, 'fake.level');
 
-        var newSummary = insertArticle(summary, article, '2.1.1');
+        const newSummary = insertArticle(summary, article, '2.1.1');
 
-        var inserted = newSummary.getByLevel('2.1.1');
-        var nextOne = newSummary.getByLevel('2.1.2');
+        const inserted = newSummary.getByLevel('2.1.1');
+        const nextOne = newSummary.getByLevel('2.1.2');
 
         expect(inserted.getTitle()).toBe('Inserted');
         expect(inserted.getLevel()).toBe('2.1.1');
@@ -60,14 +60,14 @@ describe('insertArticle', function() {
     });
 
     it('should insert an article in last position', function() {
-        var article = SummaryArticle.create({
+        const article = SummaryArticle.create({
             title: 'Inserted'
         }, 'fake.level');
 
-        var newSummary = insertArticle(summary, article, '2.2');
+        const newSummary = insertArticle(summary, article, '2.2');
 
-        var inserted = newSummary.getByLevel('2.2');
-        var previousOne = newSummary.getByLevel('2.1');
+        const inserted = newSummary.getByLevel('2.2');
+        const previousOne = newSummary.getByLevel('2.1');
 
         expect(inserted.getTitle()).toBe('Inserted');
         expect(inserted.getLevel()).toBe('2.2');
diff --git a/packages/gitbook/lib/modifiers/summary/__tests__/insertPart.js b/packages/gitbook/src/modifiers/summary/__tests__/insertPart.js
index 11c2cbc..5112931 100644
--- a/packages/gitbook/lib/modifiers/summary/__tests__/insertPart.js
+++ b/packages/gitbook/src/modifiers/summary/__tests__/insertPart.js
@@ -1,11 +1,11 @@
-var Summary = require('../../../models/summary');
-var SummaryPart = require('../../../models/summaryPart');
+const Summary = require('../../../models/summary');
+const SummaryPart = require('../../../models/summaryPart');
 
-var File = require('../../../models/file');
+const File = require('../../../models/file');
 
 describe('insertPart', function() {
-    var insertPart = require('../insertPart');
-    var summary = Summary.createFromParts(File(), [
+    const insertPart = require('../insertPart');
+    const summary = Summary.createFromParts(File(), [
         {
             articles: [
                 {
@@ -31,29 +31,29 @@ describe('insertPart', function() {
     ]);
 
     it('should insert an part at a given level', function() {
-        var part = SummaryPart.create({
+        const part = SummaryPart.create({
             title: 'Inserted'
         }, 'meaningless.level');
 
-        var newSummary = insertPart(summary, part, 1);
+        const newSummary = insertPart(summary, part, 1);
 
-        var inserted = newSummary.getPart(1);
+        const inserted = newSummary.getPart(1);
         expect(inserted.getTitle()).toBe('Inserted');
         expect(newSummary.getParts().count()).toBe(3);
 
-        var otherArticle = newSummary.getByLevel('3.1');
+        const otherArticle = newSummary.getByLevel('3.1');
         expect(otherArticle.getTitle()).toBe('2.1');
         expect(otherArticle.getLevel()).toBe('3.1');
     });
 
     it('should insert an part in last position', function() {
-        var part = SummaryPart.create({
+        const part = SummaryPart.create({
             title: 'Inserted'
         }, 'meaningless.level');
 
-        var newSummary = insertPart(summary, part, 2);
+        const newSummary = insertPart(summary, part, 2);
 
-        var inserted = newSummary.getPart(2);
+        const inserted = newSummary.getPart(2);
         expect(inserted.getTitle()).toBe('Inserted');
         expect(newSummary.getParts().count()).toBe(3);
     });
diff --git a/packages/gitbook/lib/modifiers/summary/__tests__/mergeAtLevel.js b/packages/gitbook/src/modifiers/summary/__tests__/mergeAtLevel.js
index e2635ec..e0d4a62 100644
--- a/packages/gitbook/lib/modifiers/summary/__tests__/mergeAtLevel.js
+++ b/packages/gitbook/src/modifiers/summary/__tests__/mergeAtLevel.js
@@ -1,10 +1,10 @@
-var Immutable = require('immutable');
-var Summary = require('../../../models/summary');
-var File = require('../../../models/file');
+const Immutable = require('immutable');
+const Summary = require('../../../models/summary');
+const File = require('../../../models/file');
 
 describe('mergeAtLevel', function() {
-    var mergeAtLevel = require('../mergeAtLevel');
-    var summary = Summary.createFromParts(File(), [
+    const mergeAtLevel = require('../mergeAtLevel');
+    const summary = Summary.createFromParts(File(), [
         {
             articles: [
                 {
@@ -24,9 +24,9 @@ describe('mergeAtLevel', function() {
     ]);
 
     it('should edit a part', function() {
-        var beforeChildren = summary.getByLevel('1').getArticles();
-        var newSummary = mergeAtLevel(summary, '1', {title: 'Part O'});
-        var edited = newSummary.getByLevel('1');
+        const beforeChildren = summary.getByLevel('1').getArticles();
+        const newSummary = mergeAtLevel(summary, '1', {title: 'Part O'});
+        const edited = newSummary.getByLevel('1');
 
         expect(edited.getTitle()).toBe('Part O');
         // Same children
@@ -34,9 +34,9 @@ describe('mergeAtLevel', function() {
     });
 
     it('should edit a part', function() {
-        var beforePath = summary.getByLevel('1.2').getPath();
-        var newSummary = mergeAtLevel(summary, '1.2', {title: 'Renamed article'});
-        var edited = newSummary.getByLevel('1.2');
+        const beforePath = summary.getByLevel('1.2').getPath();
+        const newSummary = mergeAtLevel(summary, '1.2', {title: 'Renamed article'});
+        const edited = newSummary.getByLevel('1.2');
 
         expect(edited.getTitle()).toBe('Renamed article');
         // Same children
diff --git a/packages/gitbook/lib/modifiers/summary/__tests__/moveArticle.js b/packages/gitbook/src/modifiers/summary/__tests__/moveArticle.js
index aed0b94..a7d111b 100644
--- a/packages/gitbook/lib/modifiers/summary/__tests__/moveArticle.js
+++ b/packages/gitbook/src/modifiers/summary/__tests__/moveArticle.js
@@ -1,10 +1,10 @@
-var Immutable = require('immutable');
-var Summary = require('../../../models/summary');
-var File = require('../../../models/file');
+const Immutable = require('immutable');
+const Summary = require('../../../models/summary');
+const File = require('../../../models/file');
 
 describe('moveArticle', function() {
-    var moveArticle = require('../moveArticle');
-    var summary = Summary.createFromParts(File(), [
+    const moveArticle = require('../moveArticle');
+    const summary = Summary.createFromParts(File(), [
         {
             articles: [
                 {
@@ -43,24 +43,24 @@ describe('moveArticle', function() {
     ]);
 
     it('should move an article to the same place', function() {
-        var newSummary = moveArticle(summary, '2.1', '2.1');
+        const newSummary = moveArticle(summary, '2.1', '2.1');
 
         expect(Immutable.is(summary, newSummary)).toBe(true);
     });
 
     it('should move an article to an previous level', function() {
-        var newSummary = moveArticle(summary, '2.2', '2.1');
-        var moved = newSummary.getByLevel('2.1');
-        var other = newSummary.getByLevel('2.2');
+        const newSummary = moveArticle(summary, '2.2', '2.1');
+        const moved = newSummary.getByLevel('2.1');
+        const other = newSummary.getByLevel('2.2');
 
         expect(moved.getTitle()).toBe('2.2');
         expect(other.getTitle()).toBe('2.1');
     });
 
     it('should move an article to a next level', function() {
-        var newSummary = moveArticle(summary, '2.1', '2.2');
-        var moved = newSummary.getByLevel('2.1');
-        var other = newSummary.getByLevel('2.2');
+        const newSummary = moveArticle(summary, '2.1', '2.2');
+        const moved = newSummary.getByLevel('2.1');
+        const other = newSummary.getByLevel('2.2');
 
         expect(moved.getTitle()).toBe('2.2');
         expect(other.getTitle()).toBe('2.1');
diff --git a/packages/gitbook/lib/modifiers/summary/__tests__/moveArticleAfter.js b/packages/gitbook/src/modifiers/summary/__tests__/moveArticleAfter.js
index c380575..446d8a4 100644
--- a/packages/gitbook/lib/modifiers/summary/__tests__/moveArticleAfter.js
+++ b/packages/gitbook/src/modifiers/summary/__tests__/moveArticleAfter.js
@@ -1,10 +1,10 @@
-var Immutable = require('immutable');
-var Summary = require('../../../models/summary');
-var File = require('../../../models/file');
+const Immutable = require('immutable');
+const Summary = require('../../../models/summary');
+const File = require('../../../models/file');
 
 describe('moveArticleAfter', function() {
-    var moveArticleAfter = require('../moveArticleAfter');
-    var summary = Summary.createFromParts(File(), [
+    const moveArticleAfter = require('../moveArticleAfter');
+    const summary = Summary.createFromParts(File(), [
         {
             articles: [
                 {
@@ -43,28 +43,28 @@ describe('moveArticleAfter', function() {
     ]);
 
     it('moving right after itself should be invariant', function() {
-        var newSummary = moveArticleAfter(summary, '2.1', '2.1');
+        const newSummary = moveArticleAfter(summary, '2.1', '2.1');
 
         expect(Immutable.is(summary, newSummary)).toBe(true);
     });
 
     it('moving after previous one should be invariant too', function() {
-        var newSummary = moveArticleAfter(summary, '2.1', '2.0');
+        const newSummary = moveArticleAfter(summary, '2.1', '2.0');
 
         expect(Immutable.is(summary, newSummary)).toBe(true);
     });
 
     it('should move an article after a previous level', function() {
-        var newSummary = moveArticleAfter(summary, '2.2', '2.0');
-        var moved = newSummary.getByLevel('2.1');
+        const newSummary = moveArticleAfter(summary, '2.2', '2.0');
+        const moved = newSummary.getByLevel('2.1');
 
         expect(moved.getTitle()).toBe('2.2');
         expect(newSummary.getByLevel('2.2').getTitle()).toBe('2.1');
     });
 
     it('should move an article after a previous and less deep level', function() {
-        var newSummary = moveArticleAfter(summary, '2.1.1', '2.0');
-        var moved = newSummary.getByLevel('2.1');
+        const newSummary = moveArticleAfter(summary, '2.1.1', '2.0');
+        const moved = newSummary.getByLevel('2.1');
 
         expect(moved.getTitle()).toBe('2.1.1');
         expect(newSummary.getByLevel('2.2.1').getTitle()).toBe('2.1.2');
@@ -72,8 +72,8 @@ describe('moveArticleAfter', function() {
     });
 
     it('should move an article after a next level', function() {
-        var newSummary = moveArticleAfter(summary, '2.1', '2.2');
-        var moved = newSummary.getByLevel('2.2');
+        const newSummary = moveArticleAfter(summary, '2.1', '2.2');
+        const moved = newSummary.getByLevel('2.2');
 
         expect(moved.getTitle()).toBe('2.1');
         expect(newSummary.getByLevel('2.1').getTitle()).toBe('2.2');
diff --git a/packages/gitbook/lib/modifiers/summary/__tests__/removeArticle.js b/packages/gitbook/src/modifiers/summary/__tests__/removeArticle.js
index b45fb49..14587ca 100644
--- a/packages/gitbook/lib/modifiers/summary/__tests__/removeArticle.js
+++ b/packages/gitbook/src/modifiers/summary/__tests__/removeArticle.js
@@ -1,9 +1,9 @@
-var Summary = require('../../../models/summary');
-var File = require('../../../models/file');
+const Summary = require('../../../models/summary');
+const File = require('../../../models/file');
 
 describe('removeArticle', function() {
-    var removeArticle = require('../removeArticle');
-    var summary = Summary.createFromParts(File(), [
+    const removeArticle = require('../removeArticle');
+    const summary = Summary.createFromParts(File(), [
         {
             articles: [
                 {
@@ -42,10 +42,10 @@ describe('removeArticle', function() {
     ]);
 
     it('should remove an article at a given level', function() {
-        var newSummary = removeArticle(summary, '2.1.1');
+        const newSummary = removeArticle(summary, '2.1.1');
 
-        var removed = newSummary.getByLevel('2.1.1');
-        var nextOne = newSummary.getByLevel('2.1.2');
+        const removed = newSummary.getByLevel('2.1.1');
+        const nextOne = newSummary.getByLevel('2.1.2');
 
         expect(removed.getTitle()).toBe('2.1.2');
         expect(nextOne).toBe(null);
diff --git a/packages/gitbook/lib/modifiers/summary/editArticleRef.js b/packages/gitbook/src/modifiers/summary/editArticleRef.js
index 7106960..c5c1868 100644
--- a/packages/gitbook/lib/modifiers/summary/editArticleRef.js
+++ b/packages/gitbook/src/modifiers/summary/editArticleRef.js
@@ -1,4 +1,4 @@
-var mergeAtLevel = require('./mergeAtLevel');
+const mergeAtLevel = require('./mergeAtLevel');
 
 /**
     Edit the ref of an article
diff --git a/packages/gitbook/lib/modifiers/summary/editArticleTitle.js b/packages/gitbook/src/modifiers/summary/editArticleTitle.js
index 4edee83..f55c97e 100644
--- a/packages/gitbook/lib/modifiers/summary/editArticleTitle.js
+++ b/packages/gitbook/src/modifiers/summary/editArticleTitle.js
@@ -1,4 +1,4 @@
-var mergeAtLevel = require('./mergeAtLevel');
+const mergeAtLevel = require('./mergeAtLevel');
 
 /**
     Edit title of an article
diff --git a/packages/gitbook/lib/modifiers/summary/editPartTitle.js b/packages/gitbook/src/modifiers/summary/editPartTitle.js
index b79ac1e..ace7058 100644
--- a/packages/gitbook/lib/modifiers/summary/editPartTitle.js
+++ b/packages/gitbook/src/modifiers/summary/editPartTitle.js
@@ -7,9 +7,9 @@
     @return {Summary}
 */
 function editPartTitle(summary, index, newTitle) {
-    var parts = summary.getParts();
+    let parts = summary.getParts();
 
-    var part = parts.get(index);
+    let part = parts.get(index);
     if (!part) {
         return summary;
     }
diff --git a/packages/gitbook/lib/modifiers/summary/index.js b/packages/gitbook/src/modifiers/summary/index.js
index f91fdb6..f91fdb6 100644
--- a/packages/gitbook/lib/modifiers/summary/index.js
+++ b/packages/gitbook/src/modifiers/summary/index.js
diff --git a/packages/gitbook/lib/modifiers/summary/indexArticleLevels.js b/packages/gitbook/src/modifiers/summary/indexArticleLevels.js
index f311f74..03c26c7 100644
--- a/packages/gitbook/lib/modifiers/summary/indexArticleLevels.js
+++ b/packages/gitbook/src/modifiers/summary/indexArticleLevels.js
@@ -8,7 +8,7 @@
 */
 function indexArticleLevels(article, baseLevel) {
     baseLevel = baseLevel || article.getLevel();
-    var articles = article.getArticles();
+    let articles = article.getArticles();
 
     articles = articles.map(function(inner, i) {
         return indexArticleLevels(inner, baseLevel + '.' + (i + 1));
@@ -16,7 +16,7 @@ function indexArticleLevels(article, baseLevel) {
 
     return article.merge({
         level: baseLevel,
-        articles: articles
+        articles
     });
 }
 
diff --git a/packages/gitbook/lib/modifiers/summary/indexLevels.js b/packages/gitbook/src/modifiers/summary/indexLevels.js
index 604e9ff..deb76da 100644
--- a/packages/gitbook/lib/modifiers/summary/indexLevels.js
+++ b/packages/gitbook/src/modifiers/summary/indexLevels.js
@@ -1,4 +1,4 @@
-var indexPartLevels = require('./indexPartLevels');
+const indexPartLevels = require('./indexPartLevels');
 
 /**
     Index all levels in the summary
@@ -7,7 +7,7 @@ var indexPartLevels = require('./indexPartLevels');
     @return {Summary}
 */
 function indexLevels(summary) {
-    var parts = summary.getParts();
+    let parts = summary.getParts();
     parts = parts.map(indexPartLevels);
 
     return summary.set('parts', parts);
diff --git a/packages/gitbook/lib/modifiers/summary/indexPartLevels.js b/packages/gitbook/src/modifiers/summary/indexPartLevels.js
index d19c70a..6e48778 100644
--- a/packages/gitbook/lib/modifiers/summary/indexPartLevels.js
+++ b/packages/gitbook/src/modifiers/summary/indexPartLevels.js
@@ -1,4 +1,4 @@
-var indexArticleLevels = require('./indexArticleLevels');
+const indexArticleLevels = require('./indexArticleLevels');
 
 /**
     Index levels in a part
@@ -8,8 +8,8 @@ var indexArticleLevels = require('./indexArticleLevels');
     @return {Part}
 */
 function indexPartLevels(part, index) {
-    var baseLevel = String(index + 1);
-    var articles = part.getArticles();
+    const baseLevel = String(index + 1);
+    let articles = part.getArticles();
 
     articles = articles.map(function(inner, i) {
         return indexArticleLevels(inner, baseLevel + '.' + (i + 1));
@@ -17,7 +17,7 @@ function indexPartLevels(part, index) {
 
     return part.merge({
         level: baseLevel,
-        articles: articles
+        articles
     });
 }
 
diff --git a/packages/gitbook/lib/modifiers/summary/insertArticle.js b/packages/gitbook/src/modifiers/summary/insertArticle.js
index 3a084b3..537f548 100644
--- a/packages/gitbook/lib/modifiers/summary/insertArticle.js
+++ b/packages/gitbook/src/modifiers/summary/insertArticle.js
@@ -1,7 +1,7 @@
-var is = require('is');
-var SummaryArticle = require('../../models/summaryArticle');
-var mergeAtLevel = require('./mergeAtLevel');
-var indexArticleLevels = require('./indexArticleLevels');
+const is = require('is');
+const SummaryArticle = require('../../models/summaryArticle');
+const mergeAtLevel = require('./mergeAtLevel');
+const indexArticleLevels = require('./indexArticleLevels');
 
 /**
     Returns a new Summary with the article at the given level, with
@@ -14,16 +14,16 @@ var indexArticleLevels = require('./indexArticleLevels');
 */
 function insertArticle(summary, article, level) {
     article = SummaryArticle(article);
-    level = is.string(level)? level : level.getLevel();
+    level = is.string(level) ? level : level.getLevel();
 
-    var parent = summary.getParent(level);
+    let parent = summary.getParent(level);
     if (!parent) {
         return summary;
     }
 
     // Find the index to insert at
-    var articles = parent.getArticles();
-    var index = getLeafIndex(level);
+    let articles = parent.getArticles();
+    const index = getLeafIndex(level);
 
     // Insert the article at the right index
     articles = articles.insert(index, article);
@@ -40,7 +40,7 @@ function insertArticle(summary, article, level) {
     @return {Number} The index of this level within its parent's children
  */
 function getLeafIndex(level) {
-    var arr = level.split('.').map(function (char) {
+    const arr = level.split('.').map(function(char) {
         return parseInt(char, 10);
     });
     return arr[arr.length - 1] - 1;
diff --git a/packages/gitbook/lib/modifiers/summary/insertPart.js b/packages/gitbook/src/modifiers/summary/insertPart.js
index 199cba7..ea99f89 100644
--- a/packages/gitbook/lib/modifiers/summary/insertPart.js
+++ b/packages/gitbook/src/modifiers/summary/insertPart.js
@@ -1,5 +1,5 @@
-var SummaryPart = require('../../models/summaryPart');
-var indexLevels = require('./indexLevels');
+const SummaryPart = require('../../models/summaryPart');
+const indexLevels = require('./indexLevels');
 
 /**
     Returns a new Summary with a part inserted at given index
@@ -12,7 +12,7 @@ var indexLevels = require('./indexLevels');
 function insertPart(summary, part, index) {
     part = SummaryPart(part);
 
-    var parts = summary.getParts().insert(index, part);
+    const parts = summary.getParts().insert(index, part);
     return indexLevels(summary.set('parts', parts));
 }
 
diff --git a/packages/gitbook/lib/modifiers/summary/mergeAtLevel.js b/packages/gitbook/src/modifiers/summary/mergeAtLevel.js
index 9a95ffc..ea01763 100644
--- a/packages/gitbook/lib/modifiers/summary/mergeAtLevel.js
+++ b/packages/gitbook/src/modifiers/summary/mergeAtLevel.js
@@ -9,14 +9,14 @@
 */
 function editArticleInList(articles, level, newArticle) {
     return articles.map(function(article) {
-        var articleLevel = article.getLevel();
+        const articleLevel = article.getLevel();
 
         if (articleLevel === level) {
             // it is the article to edit
             return article.merge(newArticle);
         } else if (level.indexOf(articleLevel) === 0) {
             // it is a parent
-            var articles = editArticleInList(article.getArticles(), level, newArticle);
+            const articles = editArticleInList(article.getArticles(), level, newArticle);
             return article.set('articles', articles);
         } else {
             // This is not the article you are looking for
@@ -35,7 +35,7 @@ function editArticleInList(articles, level, newArticle) {
     @return {Part}
 */
 function editArticleInPart(part, level, newArticle) {
-    var articles = part.getArticles();
+    let articles = part.getArticles();
     articles = editArticleInList(articles, level, newArticle);
 
     return part.set('articles', articles);
@@ -51,16 +51,16 @@ function editArticleInPart(part, level, newArticle) {
     @return {Summary}
 */
 function mergeAtLevel(summary, level, newValue) {
-    var levelParts = level.split('.');
-    var partIndex = Number(levelParts[0]) -1;
+    const levelParts = level.split('.');
+    const partIndex = Number(levelParts[0]) - 1;
 
-    var parts = summary.getParts();
-    var part = parts.get(partIndex);
+    let parts = summary.getParts();
+    let part = parts.get(partIndex);
     if (!part) {
         return summary;
     }
 
-    var isEditingPart = levelParts.length < 2;
+    const isEditingPart = levelParts.length < 2;
     if (isEditingPart) {
         part = part.merge(newValue);
     } else {
diff --git a/packages/gitbook/lib/modifiers/summary/moveArticle.js b/packages/gitbook/src/modifiers/summary/moveArticle.js
index 5cb1868..29d4748 100644
--- a/packages/gitbook/lib/modifiers/summary/moveArticle.js
+++ b/packages/gitbook/src/modifiers/summary/moveArticle.js
@@ -1,6 +1,6 @@
-var is = require('is');
-var removeArticle = require('./removeArticle');
-var insertArticle = require('./insertArticle');
+const is = require('is');
+const removeArticle = require('./removeArticle');
+const insertArticle = require('./insertArticle');
 
 /**
     Returns a new summary, with the given article removed from its
@@ -13,12 +13,12 @@ var insertArticle = require('./insertArticle');
 */
 function moveArticle(summary, origin, target) {
     // Coerce to level
-    var originLevel = is.string(origin)? origin : origin.getLevel();
-    var targetLevel = is.string(target)? target : target.getLevel();
-    var article = summary.getByLevel(originLevel);
+    const originLevel = is.string(origin) ? origin : origin.getLevel();
+    const targetLevel = is.string(target) ? target : target.getLevel();
+    const article = summary.getByLevel(originLevel);
 
     // Remove first
-    var removed = removeArticle(summary, originLevel);
+    const removed = removeArticle(summary, originLevel);
     return insertArticle(removed, article, targetLevel);
 }
 
diff --git a/packages/gitbook/lib/modifiers/summary/moveArticleAfter.js b/packages/gitbook/src/modifiers/summary/moveArticleAfter.js
index e268f73..a1ed28f 100644
--- a/packages/gitbook/lib/modifiers/summary/moveArticleAfter.js
+++ b/packages/gitbook/src/modifiers/summary/moveArticleAfter.js
@@ -1,6 +1,6 @@
-var is = require('is');
-var removeArticle = require('./removeArticle');
-var insertArticle = require('./insertArticle');
+const is = require('is');
+const removeArticle = require('./removeArticle');
+const insertArticle = require('./insertArticle');
 
 /**
     Returns a new summary, with the an article moved after another
@@ -14,20 +14,20 @@ var insertArticle = require('./insertArticle');
 */
 function moveArticleAfter(summary, origin, afterTarget) {
     // Coerce to level
-    var originLevel = is.string(origin)? origin : origin.getLevel();
-    var afterTargetLevel = is.string(afterTarget)? afterTarget : afterTarget.getLevel();
-    var article = summary.getByLevel(originLevel);
+    const originLevel = is.string(origin) ? origin : origin.getLevel();
+    const afterTargetLevel = is.string(afterTarget) ? afterTarget : afterTarget.getLevel();
+    const article = summary.getByLevel(originLevel);
 
-    var targetLevel = increment(afterTargetLevel);
+    const targetLevel = increment(afterTargetLevel);
 
     if (targetLevel < origin) {
         // Remove first
-        var removed = removeArticle(summary, originLevel);
+        const removed = removeArticle(summary, originLevel);
         // Insert then
         return insertArticle(removed, article, targetLevel);
     } else {
         // Insert right after first
-        var inserted = insertArticle(summary, article, targetLevel);
+        const inserted = insertArticle(summary, article, targetLevel);
         // Remove old one
         return removeArticle(inserted, originLevel);
     }
@@ -38,7 +38,7 @@ function moveArticleAfter(summary, origin, afterTarget) {
     @return {Array<Number>}
  */
 function levelToArray(l) {
-    return l.split('.').map(function (char) {
+    return l.split('.').map(function(char) {
         return parseInt(char, 10);
     });
 }
diff --git a/packages/gitbook/lib/modifiers/summary/removeArticle.js b/packages/gitbook/src/modifiers/summary/removeArticle.js
index 8a30d0a..0c4cd33 100644
--- a/packages/gitbook/lib/modifiers/summary/removeArticle.js
+++ b/packages/gitbook/src/modifiers/summary/removeArticle.js
@@ -1,6 +1,6 @@
-var is = require('is');
-var mergeAtLevel = require('./mergeAtLevel');
-var indexArticleLevels = require('./indexArticleLevels');
+const is = require('is');
+const mergeAtLevel = require('./mergeAtLevel');
+const indexArticleLevels = require('./indexArticleLevels');
 
 /**
     Remove an article from a level.
@@ -11,13 +11,13 @@ var indexArticleLevels = require('./indexArticleLevels');
 */
 function removeArticle(summary, level) {
     // Coerce to level
-    level = is.string(level)? level : level.getLevel();
+    level = is.string(level) ? level : level.getLevel();
 
-    var parent = summary.getParent(level);
+    let parent = summary.getParent(level);
 
-    var articles = parent.getArticles();
+    let articles = parent.getArticles();
     // Find the index to remove
-    var index = articles.findIndex(function(art) {
+    const index = articles.findIndex(function(art) {
         return art.getLevel() === level;
     });
     if (index === -1) {
diff --git a/packages/gitbook/lib/modifiers/summary/removePart.js b/packages/gitbook/src/modifiers/summary/removePart.js
index 2f8affc..30502dc 100644
--- a/packages/gitbook/lib/modifiers/summary/removePart.js
+++ b/packages/gitbook/src/modifiers/summary/removePart.js
@@ -1,4 +1,4 @@
-var indexLevels = require('./indexLevels');
+const indexLevels = require('./indexLevels');
 
 /**
     Remove a part at given index
@@ -8,7 +8,7 @@ var indexLevels = require('./indexLevels');
     @return {Summary}
 */
 function removePart(summary, index) {
-    var parts = summary.getParts().remove(index);
+    const parts = summary.getParts().remove(index);
     return indexLevels(summary.set('parts', parts));
 }
 
diff --git a/packages/gitbook/lib/modifiers/summary/unshiftArticle.js b/packages/gitbook/src/modifiers/summary/unshiftArticle.js
index d1ebc05..c5810f0 100644
--- a/packages/gitbook/lib/modifiers/summary/unshiftArticle.js
+++ b/packages/gitbook/src/modifiers/summary/unshiftArticle.js
@@ -1,7 +1,7 @@
-var SummaryArticle = require('../../models/summaryArticle');
-var SummaryPart = require('../../models/summaryPart');
+const SummaryArticle = require('../../models/summaryArticle');
+const SummaryPart = require('../../models/summaryPart');
 
-var indexLevels = require('./indexLevels');
+const indexLevels = require('./indexLevels');
 
 /**
     Insert an article at the beginning of summary
@@ -13,10 +13,10 @@ var indexLevels = require('./indexLevels');
 function unshiftArticle(summary, article) {
     article = SummaryArticle(article);
 
-    var parts = summary.getParts();
-    var part = parts.get(0) || SummaryPart();
+    let parts = summary.getParts();
+    let part = parts.get(0) || SummaryPart();
 
-    var articles = part.getArticles();
+    let articles = part.getArticles();
     articles = articles.unshift(article);
     part = part.set('articles', articles);
 
diff --git a/packages/gitbook/lib/output/__tests__/createMock.js b/packages/gitbook/src/output/__tests__/createMock.js
index f21c544..09b93da 100644
--- a/packages/gitbook/lib/output/__tests__/createMock.js
+++ b/packages/gitbook/src/output/__tests__/createMock.js
@@ -1,10 +1,10 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var Output = require('../../models/output');
-var Book = require('../../models/book');
-var parseBook = require('../../parse/parseBook');
-var createMockFS = require('../../fs/mock');
-var preparePlugins = require('../preparePlugins');
+const Output = require('../../models/output');
+const Book = require('../../models/book');
+const parseBook = require('../../parse/parseBook');
+const createMockFS = require('../../fs/mock');
+const preparePlugins = require('../preparePlugins');
 
 /**
  * Create an output using a generator
@@ -16,9 +16,9 @@ var preparePlugins = require('../preparePlugins');
  * @return {Promise<Output>}
  */
 function createMockOutput(generator, files, options) {
-    var fs = createMockFS(files);
-    var book = Book.createForFS(fs);
-    var state = generator.State? generator.State({}) : Immutable.Map();
+    const fs = createMockFS(files);
+    let book = Book.createForFS(fs);
+    const state = generator.State ? generator.State({}) : Immutable.Map();
 
     book = book.setLogLevel('disabled');
     options = generator.Options(options);
@@ -27,8 +27,8 @@ function createMockOutput(generator, files, options) {
     .then(function(resultBook) {
         return new Output({
             book:      resultBook,
-            options:   options,
-            state:     state,
+            options,
+            state,
             generator: generator.name
         });
     })
diff --git a/packages/gitbook/lib/output/__tests__/ebook.js b/packages/gitbook/src/output/__tests__/ebook.js
index 9266e9f..425ab6b 100644
--- a/packages/gitbook/lib/output/__tests__/ebook.js
+++ b/packages/gitbook/src/output/__tests__/ebook.js
@@ -1,5 +1,5 @@
-var generateMock = require('./generateMock');
-var EbookGenerator = require('../ebook');
+const generateMock = require('./generateMock');
+const EbookGenerator = require('../ebook');
 
 describe('EbookGenerator', function() {
 
diff --git a/packages/gitbook/lib/output/__tests__/generateMock.js b/packages/gitbook/src/output/__tests__/generateMock.js
index 691ee2d..a0be244 100644
--- a/packages/gitbook/lib/output/__tests__/generateMock.js
+++ b/packages/gitbook/src/output/__tests__/generateMock.js
@@ -1,9 +1,9 @@
-var tmp = require('tmp');
+const tmp = require('tmp');
 
-var Book = require('../../models/book');
-var createMockFS = require('../../fs/mock');
-var parseBook = require('../../parse/parseBook');
-var generateBook = require('../generateBook');
+const Book = require('../../models/book');
+const createMockFS = require('../../fs/mock');
+const parseBook = require('../../parse/parseBook');
+const generateBook = require('../generateBook');
 
 /**
  * Generate a book using a generator
@@ -16,13 +16,13 @@ var generateBook = require('../generateBook');
  * @return {Promise<String>}
  */
 function generateMock(Generator, files) {
-    var fs = createMockFS(files);
-    var book = Book.createForFS(fs);
-    var dir;
+    const fs = createMockFS(files);
+    let book = Book.createForFS(fs);
+    let dir;
 
     try {
         dir = tmp.dirSync();
-    } catch(err) {
+    } catch (err) {
         throw err;
     }
 
diff --git a/packages/gitbook/lib/output/__tests__/json.js b/packages/gitbook/src/output/__tests__/json.js
index 12ab567..d4992ec 100644
--- a/packages/gitbook/lib/output/__tests__/json.js
+++ b/packages/gitbook/src/output/__tests__/json.js
@@ -1,5 +1,5 @@
-var generateMock = require('./generateMock');
-var JSONGenerator = require('../json');
+const generateMock = require('./generateMock');
+const JSONGenerator = require('../json');
 
 describe('JSONGenerator', function() {
 
diff --git a/packages/gitbook/lib/output/__tests__/website.js b/packages/gitbook/src/output/__tests__/website.js
index 1f8c3c0..d39842f 100644
--- a/packages/gitbook/lib/output/__tests__/website.js
+++ b/packages/gitbook/src/output/__tests__/website.js
@@ -1,6 +1,6 @@
-var fs = require('fs');
-var generateMock = require('./generateMock');
-var WebsiteGenerator = require('../website');
+const fs = require('fs');
+const generateMock = require('./generateMock');
+const WebsiteGenerator = require('../website');
 
 describe('WebsiteGenerator', function() {
 
@@ -14,7 +14,7 @@ describe('WebsiteGenerator', function() {
     });
 
     describe('Glossary', function() {
-        var folder;
+        let folder;
 
         before(function() {
             return generateMock(WebsiteGenerator, {
@@ -35,12 +35,12 @@ describe('WebsiteGenerator', function() {
         });
 
         it('should correctly resolve glossary links in README', function() {
-            var html = fs.readFileSync(folder + '/index.html', 'utf8');
+            const html = fs.readFileSync(folder + '/index.html', 'utf8');
             expect(html).toHaveDOMElement('.page-inner a[href="GLOSSARY.html#hello"]');
         });
 
         it('should correctly resolve glossary links in directory', function() {
-            var html = fs.readFileSync(folder + '/folder/page.html', 'utf8');
+            const html = fs.readFileSync(folder + '/folder/page.html', 'utf8');
             expect(html).toHaveDOMElement('.page-inner a[href="../GLOSSARY.html#hello"]');
         });
 
@@ -54,7 +54,7 @@ describe('WebsiteGenerator', function() {
                 expect(folder).toHaveFile('custom.html');
                 expect(folder).toNotHaveFile('GLOSSARY.html');
 
-                var html = fs.readFileSync(folder + '/index.html', 'utf8');
+                const html = fs.readFileSync(folder + '/index.html', 'utf8');
                 expect(html).toHaveDOMElement('.page-inner a[href="custom.html#hello"]');
             });
         });
diff --git a/packages/gitbook/lib/output/callHook.js b/packages/gitbook/src/output/callHook.js
index 4914e52..2180102 100644
--- a/packages/gitbook/lib/output/callHook.js
+++ b/packages/gitbook/src/output/callHook.js
@@ -1,6 +1,6 @@
-var Promise = require('../utils/promise');
-var timing = require('../utils/timing');
-var Api = require('../api');
+const Promise = require('../utils/promise');
+const timing = require('../utils/timing');
+const Api = require('../api');
 
 function defaultGetArgument() {
     return undefined;
@@ -23,13 +23,13 @@ function callHook(name, getArgument, handleResult, output) {
     getArgument = getArgument || defaultGetArgument;
     handleResult = handleResult || defaultHandleResult;
 
-    var logger = output.getLogger();
-    var plugins = output.getPlugins();
+    const logger = output.getLogger();
+    const plugins = output.getPlugins();
 
     logger.debug.ln('calling hook "' + name + '"');
 
     // Create the JS context for plugins
-    var context = Api.encodeGlobal(output);
+    const context = Api.encodeGlobal(output);
 
     return timing.measure(
         'call.hook.' + name,
@@ -40,7 +40,7 @@ function callHook(name, getArgument, handleResult, output) {
         // Call the hooks in serie
         .then(function(arg) {
             return Promise.reduce(plugins, function(prev, plugin) {
-                var hook = plugin.getHook(name);
+                const hook = plugin.getHook(name);
                 if (!hook) {
                     return prev;
                 }
diff --git a/packages/gitbook/lib/output/callPageHook.js b/packages/gitbook/src/output/callPageHook.js
index c66cef0..af249c9 100644
--- a/packages/gitbook/lib/output/callPageHook.js
+++ b/packages/gitbook/src/output/callPageHook.js
@@ -1,5 +1,5 @@
-var Api = require('../api');
-var callHook = require('./callHook');
+const Api = require('../api');
+const callHook = require('./callHook');
 
 /**
     Call a hook for a specific page
diff --git a/packages/gitbook/src/output/createTemplateEngine.js b/packages/gitbook/src/output/createTemplateEngine.js
new file mode 100644
index 0000000..03e7d84
--- /dev/null
+++ b/packages/gitbook/src/output/createTemplateEngine.js
@@ -0,0 +1,45 @@
+const Templating = require('../templating');
+const TemplateEngine = require('../models/templateEngine');
+
+const Api = require('../api');
+const Plugins = require('../plugins');
+
+const defaultBlocks = require('../constants/defaultBlocks');
+const defaultFilters = require('../constants/defaultFilters');
+
+/**
+    Create template engine for an output.
+    It adds default filters/blocks, then add the ones from plugins
+
+    @param {Output} output
+    @return {TemplateEngine}
+*/
+function createTemplateEngine(output) {
+    const plugins = output.getPlugins();
+    const book = output.getBook();
+    const rootFolder = book.getContentRoot();
+    const logger = book.getLogger();
+
+    let filters = Plugins.listFilters(plugins);
+    let blocks = Plugins.listBlocks(plugins);
+
+    // Extend with default
+    blocks = defaultBlocks.merge(blocks);
+    filters = defaultFilters.merge(filters);
+
+    // Create loader
+    const transformFn = Templating.replaceShortcuts.bind(null, blocks);
+    const loader = new Templating.ConrefsLoader(rootFolder, transformFn, logger);
+
+    // Create API context
+    const context = Api.encodeGlobal(output);
+
+    return new TemplateEngine({
+        filters,
+        blocks,
+        loader,
+        context
+    });
+}
+
+module.exports = createTemplateEngine;
diff --git a/packages/gitbook/lib/output/ebook/getConvertOptions.js b/packages/gitbook/src/output/ebook/getConvertOptions.js
index bc80493..b37c68e 100644
--- a/packages/gitbook/lib/output/ebook/getConvertOptions.js
+++ b/packages/gitbook/src/output/ebook/getConvertOptions.js
@@ -1,8 +1,8 @@
-var extend = require('extend');
+const extend = require('extend');
 
-var Promise = require('../../utils/promise');
-var getPDFTemplate = require('./getPDFTemplate');
-var getCoverPath = require('./getCoverPath');
+const Promise = require('../../utils/promise');
+const getPDFTemplate = require('./getPDFTemplate');
+const getCoverPath = require('./getCoverPath');
 
 /**
     Generate options for ebook-convert
@@ -11,16 +11,16 @@ var getCoverPath = require('./getCoverPath');
     @return {Promise<Object>}
 */
 function getConvertOptions(output) {
-    var options = output.getOptions();
-    var format = options.get('format');
+    const options = output.getOptions();
+    const format = options.get('format');
 
-    var book = output.getBook();
-    var config = book.getConfig();
+    const book = output.getBook();
+    const config = book.getConfig();
 
     return Promise()
     .then(function() {
-        var coverPath = getCoverPath(output);
-        var options = {
+        const coverPath = getCoverPath(output);
+        let options = {
             '--cover':                      coverPath,
             '--title':                      config.getValue('title'),
             '--comments':                   config.getValue('description'),
@@ -36,7 +36,7 @@ function getConvertOptions(output) {
             '--max-levels':                 '1',
             '--no-chapters-in-toc':         true,
             '--breadth-first':              true,
-            '--dont-split-on-page-breaks':  format === 'epub'? true : undefined
+            '--dont-split-on-page-breaks':  format === 'epub' ? true : undefined
         };
 
         if (format !== 'pdf') {
@@ -48,7 +48,7 @@ function getConvertOptions(output) {
             getPDFTemplate(output, 'footer')
         ])
         .spread(function(headerTpl, footerTpl) {
-            var pdfOptions = config.getValue('pdf').toJS();
+            const pdfOptions = config.getValue('pdf').toJS();
 
             return options = extend(options, {
                 '--chapter-mark':           String(pdfOptions.chapterMark),
diff --git a/packages/gitbook/lib/output/ebook/getCoverPath.js b/packages/gitbook/src/output/ebook/getCoverPath.js
index ab6b579..cf18c8d 100644
--- a/packages/gitbook/lib/output/ebook/getCoverPath.js
+++ b/packages/gitbook/src/output/ebook/getCoverPath.js
@@ -1,5 +1,5 @@
-var path = require('path');
-var fs = require('../../utils/fs');
+const path = require('path');
+const fs = require('../../utils/fs');
 
 /**
     Resolve path to cover file to use
@@ -8,13 +8,13 @@ var fs = require('../../utils/fs');
     @return {String}
 */
 function getCoverPath(output) {
-    var outputRoot = output.getRoot();
-    var book = output.getBook();
-    var config = book.getConfig();
-    var coverName = config.getValue('cover', 'cover.jpg');
+    const outputRoot = output.getRoot();
+    const book = output.getBook();
+    const config = book.getConfig();
+    const coverName = config.getValue('cover', 'cover.jpg');
 
     // Resolve to absolute
-    var cover = fs.pickFile(outputRoot, coverName);
+    let cover = fs.pickFile(outputRoot, coverName);
     if (cover) {
         return cover;
     }
diff --git a/packages/gitbook/lib/output/ebook/getPDFTemplate.js b/packages/gitbook/src/output/ebook/getPDFTemplate.js
index b767daf..c0faed3 100644
--- a/packages/gitbook/lib/output/ebook/getPDFTemplate.js
+++ b/packages/gitbook/src/output/ebook/getPDFTemplate.js
@@ -1,9 +1,9 @@
-var juice = require('juice');
+const juice = require('juice');
 
-var WebsiteGenerator = require('../website');
-var JSONUtils = require('../../json');
-var Templating = require('../../templating');
-var Promise = require('../../utils/promise');
+const WebsiteGenerator = require('../website');
+const JSONUtils = require('../../json');
+const Templating = require('../../templating');
+const Promise = require('../../utils/promise');
 
 
 /**
@@ -14,12 +14,12 @@ var Promise = require('../../utils/promise');
     @return {String}
 */
 function getPDFTemplate(output, type) {
-    var filePath = 'pdf_' + type + '.html';
-    var outputRoot = output.getRoot();
-    var engine = WebsiteGenerator.createTemplateEngine(output, filePath);
+    const filePath = 'pdf_' + type + '.html';
+    const outputRoot = output.getRoot();
+    const engine = WebsiteGenerator.createTemplateEngine(output, filePath);
 
     // Generate context
-    var context = JSONUtils.encodeOutput(output);
+    const context = JSONUtils.encodeOutput(output);
     context.page = {
         num: '_PAGENUM_',
         title: '_SECTION_'
diff --git a/packages/gitbook/lib/output/ebook/index.js b/packages/gitbook/src/output/ebook/index.js
index 786a10a..c5c07c2 100644
--- a/packages/gitbook/lib/output/ebook/index.js
+++ b/packages/gitbook/src/output/ebook/index.js
@@ -1,5 +1,5 @@
-var extend = require('extend');
-var WebsiteGenerator = require('../website');
+const extend = require('extend');
+const WebsiteGenerator = require('../website');
 
 module.exports = extend({}, WebsiteGenerator, {
     name: 'ebook',
diff --git a/packages/gitbook/lib/output/ebook/onFinish.js b/packages/gitbook/src/output/ebook/onFinish.js
index 7f21548..adff798 100644
--- a/packages/gitbook/lib/output/ebook/onFinish.js
+++ b/packages/gitbook/src/output/ebook/onFinish.js
@@ -1,15 +1,15 @@
-var path = require('path');
+const path = require('path');
 
-var WebsiteGenerator = require('../website');
-var JSONUtils = require('../../json');
-var Templating = require('../../templating');
-var Promise = require('../../utils/promise');
-var error = require('../../utils/error');
-var command = require('../../utils/command');
-var writeFile = require('../helper/writeFile');
+const WebsiteGenerator = require('../website');
+const JSONUtils = require('../../json');
+const Templating = require('../../templating');
+const Promise = require('../../utils/promise');
+const error = require('../../utils/error');
+const command = require('../../utils/command');
+const writeFile = require('../helper/writeFile');
 
-var getConvertOptions = require('./getConvertOptions');
-var SUMMARY_FILE = 'SUMMARY.html';
+const getConvertOptions = require('./getConvertOptions');
+const SUMMARY_FILE = 'SUMMARY.html';
 
 /**
     Write the SUMMARY.html
@@ -18,12 +18,12 @@ var SUMMARY_FILE = 'SUMMARY.html';
     @return {Output}
 */
 function writeSummary(output) {
-    var options = output.getOptions();
-    var prefix = options.get('prefix');
+    const options = output.getOptions();
+    const prefix = options.get('prefix');
 
-    var filePath = SUMMARY_FILE;
-    var engine = WebsiteGenerator.createTemplateEngine(output, filePath);
-    var context = JSONUtils.encodeOutput(output);
+    const filePath = SUMMARY_FILE;
+    const engine = WebsiteGenerator.createTemplateEngine(output, filePath);
+    const context = JSONUtils.encodeOutput(output);
 
     // Render the theme
     return Templating.renderFile(engine, prefix + '/summary.html', context)
@@ -41,10 +41,10 @@ function writeSummary(output) {
     @return {Output}
 */
 function runEbookConvert(output) {
-    var logger = output.getLogger();
-    var options = output.getOptions();
-    var format = options.get('format');
-    var outputFolder = output.getRoot();
+    const logger = output.getLogger();
+    const options = output.getOptions();
+    const format = options.get('format');
+    const outputFolder = output.getRoot();
 
     if (!format) {
         return Promise(output);
@@ -52,7 +52,7 @@ function runEbookConvert(output) {
 
     return getConvertOptions(output)
     .then(function(options) {
-        var cmd = [
+        const cmd = [
             'ebook-convert',
             path.resolve(outputFolder, SUMMARY_FILE),
             path.resolve(outputFolder, 'index.' + format),
diff --git a/packages/gitbook/lib/output/ebook/onPage.js b/packages/gitbook/src/output/ebook/onPage.js
index b7b9b42..520d296 100644
--- a/packages/gitbook/lib/output/ebook/onPage.js
+++ b/packages/gitbook/src/output/ebook/onPage.js
@@ -1,5 +1,5 @@
-var WebsiteGenerator = require('../website');
-var Modifiers = require('../modifiers');
+const WebsiteGenerator = require('../website');
+const Modifiers = require('../modifiers');
 
 /**
     Write a page for ebook output
@@ -8,7 +8,7 @@ var Modifiers = require('../modifiers');
     @param {Output}
 */
 function onPage(output, page) {
-    var options = output.getOptions();
+    const options = output.getOptions();
 
     // Inline assets
     return Modifiers.modifyHTML(page, [
diff --git a/packages/gitbook/lib/output/ebook/options.js b/packages/gitbook/src/output/ebook/options.js
index ea7b8b4..4156fac 100644
--- a/packages/gitbook/lib/output/ebook/options.js
+++ b/packages/gitbook/src/output/ebook/options.js
@@ -1,6 +1,6 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var Options = Immutable.Record({
+const Options = Immutable.Record({
     // Root folder for the output
     root:               String(),
 
diff --git a/packages/gitbook/lib/output/generateAssets.js b/packages/gitbook/src/output/generateAssets.js
index 7a6e104..2129553 100644
--- a/packages/gitbook/lib/output/generateAssets.js
+++ b/packages/gitbook/src/output/generateAssets.js
@@ -1,4 +1,4 @@
-var Promise = require('../utils/promise');
+const Promise = require('../utils/promise');
 
 /**
     Output all assets using a generator
@@ -8,8 +8,8 @@ var Promise = require('../utils/promise');
     @return {Promise<Output>}
 */
 function generateAssets(generator, output) {
-    var assets = output.getAssets();
-    var logger = output.getLogger();
+    const assets = output.getAssets();
+    const logger = output.getLogger();
 
     // Is generator ignoring assets?
     if (!generator.onAsset) {
diff --git a/packages/gitbook/lib/output/generateBook.js b/packages/gitbook/src/output/generateBook.js
index 46712bd..ea8c78e 100644
--- a/packages/gitbook/lib/output/generateBook.js
+++ b/packages/gitbook/src/output/generateBook.js
@@ -1,16 +1,16 @@
-var path = require('path');
-var Immutable = require('immutable');
+const path = require('path');
+const Immutable = require('immutable');
 
-var Output = require('../models/output');
-var Promise = require('../utils/promise');
-var fs = require('../utils/fs');
+const Output = require('../models/output');
+const Promise = require('../utils/promise');
+const fs = require('../utils/fs');
 
-var callHook = require('./callHook');
-var preparePlugins = require('./preparePlugins');
-var preparePages = require('./preparePages');
-var prepareAssets = require('./prepareAssets');
-var generateAssets = require('./generateAssets');
-var generatePages = require('./generatePages');
+const callHook = require('./callHook');
+const preparePlugins = require('./preparePlugins');
+const preparePages = require('./preparePages');
+const prepareAssets = require('./prepareAssets');
+const generateAssets = require('./generateAssets');
+const generatePages = require('./generatePages');
 
 /**
  * Process an output to generate the book
@@ -29,15 +29,15 @@ function processOutput(generator, startOutput) {
         callHook.bind(null,
             'config',
             function(output) {
-                var book = output.getBook();
-                var config = book.getConfig();
-                var values = config.getValues();
+                const book = output.getBook();
+                const config = book.getConfig();
+                const values = config.getValues();
 
                 return values.toJS();
             },
             function(output, result) {
-                var book = output.getBook();
-                var config = book.getConfig();
+                let book = output.getBook();
+                let config = book.getConfig();
 
                 config = config.updateValues(result);
                 book = book.set('config', config);
@@ -70,28 +70,28 @@ function processOutput(generator, startOutput) {
     .then(generatePages.bind(null, generator))
 
     .tap(function(output) {
-        var book = output.getBook();
+        const book = output.getBook();
 
         if (!book.isMultilingual()) {
             return;
         }
 
-        var logger = book.getLogger();
-        var books = book.getBooks();
-        var outputRoot = output.getRoot();
-        var plugins = output.getPlugins();
-        var state = output.getState();
-        var options = output.getOptions();
+        const logger = book.getLogger();
+        const books = book.getBooks();
+        const outputRoot = output.getRoot();
+        const plugins = output.getPlugins();
+        const state = output.getState();
+        const options = output.getOptions();
 
         return Promise.forEach(books, function(langBook) {
             // Inherits plugins list, options and state
-            var langOptions = options.set('root', path.join(outputRoot, langBook.getLanguage()));
-            var langOutput = new Output({
+            const langOptions = options.set('root', path.join(outputRoot, langBook.getLanguage()));
+            const langOutput = new Output({
                 book:       langBook,
                 options:    langOptions,
-                state:      state,
+                state,
                 generator:  generator.name,
-                plugins:    plugins
+                plugins
             });
 
             logger.info.ln('');
@@ -154,22 +154,22 @@ function processOutput(generator, startOutput) {
  */
 function generateBook(generator, book, options) {
     options = generator.Options(options);
-    var state = generator.State? generator.State({}) : Immutable.Map();
-    var start = Date.now();
+    const state = generator.State ? generator.State({}) : Immutable.Map();
+    const start = Date.now();
 
     return Promise(
         new Output({
-            book: book,
-            options: options,
-            state: state,
+            book,
+            options,
+            state,
             generator: generator.name
         })
     )
 
     // Cleanup output folder
     .then(function(output) {
-        var logger = output.getLogger();
-        var rootFolder = output.getRoot();
+        const logger = output.getLogger();
+        const rootFolder = output.getRoot();
 
         logger.debug.ln('cleanup folder "' + rootFolder + '"');
         return fs.ensureFolder(rootFolder)
@@ -180,9 +180,9 @@ function generateBook(generator, book, options) {
 
     // Log duration and end message
     .then(function(output) {
-        var logger = output.getLogger();
-        var end = Date.now();
-        var duration = (end - start)/1000;
+        const logger = output.getLogger();
+        const end = Date.now();
+        const duration = (end - start) / 1000;
 
         logger.info.ok('generation finished with success in ' + duration.toFixed(1) + 's !');
 
diff --git a/packages/gitbook/lib/output/generatePage.js b/packages/gitbook/src/output/generatePage.js
index 090a870..0fc99a3 100644
--- a/packages/gitbook/lib/output/generatePage.js
+++ b/packages/gitbook/src/output/generatePage.js
@@ -1,13 +1,13 @@
-var path = require('path');
+const path = require('path');
 
-var Promise = require('../utils/promise');
-var error = require('../utils/error');
-var timing = require('../utils/timing');
+const Promise = require('../utils/promise');
+const error = require('../utils/error');
+const timing = require('../utils/timing');
 
-var Templating = require('../templating');
-var JSONUtils = require('../json');
-var createTemplateEngine = require('./createTemplateEngine');
-var callPageHook = require('./callPageHook');
+const Templating = require('../templating');
+const JSONUtils = require('../json');
+const createTemplateEngine = require('./createTemplateEngine');
+const callPageHook = require('./callPageHook');
 
 /**
  * Prepare and generate HTML for a page
@@ -17,17 +17,17 @@ var callPageHook = require('./callPageHook');
  * @return {Promise<Page>}
  */
 function generatePage(output, page) {
-    var book = output.getBook();
-    var engine = createTemplateEngine(output);
+    const book = output.getBook();
+    const engine = createTemplateEngine(output);
 
     return timing.measure(
         'page.generate',
         Promise(page)
         .then(function(resultPage) {
-            var file = resultPage.getFile();
-            var filePath = file.getPath();
-            var parser = file.getParser();
-            var context = JSONUtils.encodeOutputWithPage(output, resultPage);
+            const file = resultPage.getFile();
+            const filePath = file.getPath();
+            const parser = file.getParser();
+            const context = JSONUtils.encodeOutputWithPage(output, resultPage);
 
             if (!parser) {
                 return Promise.reject(error.FileNotParsableError({
@@ -45,12 +45,12 @@ function generatePage(output, page) {
 
             // Render templating syntax
             .then(function(content) {
-                var absoluteFilePath = path.join(book.getContentRoot(), filePath);
+                const absoluteFilePath = path.join(book.getContentRoot(), filePath);
                 return Templating.render(engine, absoluteFilePath, content, context);
             })
 
             .then(function(output) {
-                var content = output.getContent();
+                const content = output.getContent();
 
                 return parser.parsePage(content)
                 .then(function(result) {
diff --git a/packages/gitbook/lib/output/generatePages.js b/packages/gitbook/src/output/generatePages.js
index 73c5c09..21b6610 100644
--- a/packages/gitbook/lib/output/generatePages.js
+++ b/packages/gitbook/src/output/generatePages.js
@@ -1,5 +1,5 @@
-var Promise = require('../utils/promise');
-var generatePage = require('./generatePage');
+const Promise = require('../utils/promise');
+const generatePage = require('./generatePage');
 
 /**
     Output all pages using a generator
@@ -9,8 +9,8 @@ var generatePage = require('./generatePage');
     @return {Promise<Output>}
 */
 function generatePages(generator, output) {
-    var pages = output.getPages();
-    var logger = output.getLogger();
+    const pages = output.getPages();
+    const logger = output.getLogger();
 
     // Is generator ignoring assets?
     if (!generator.onPage) {
@@ -18,7 +18,7 @@ function generatePages(generator, output) {
     }
 
     return Promise.reduce(pages, function(out, page) {
-        var file = page.getFile();
+        const file = page.getFile();
 
         logger.debug.ln('generate page "' + file.getPath() + '"');
 
diff --git a/packages/gitbook/lib/output/getModifiers.js b/packages/gitbook/src/output/getModifiers.js
index bb44e80..df32fcb 100644
--- a/packages/gitbook/lib/output/getModifiers.js
+++ b/packages/gitbook/src/output/getModifiers.js
@@ -1,12 +1,12 @@
-var Modifiers = require('./modifiers');
-var resolveFileToURL = require('./helper/resolveFileToURL');
-var Api = require('../api');
-var Plugins = require('../plugins');
-var Promise = require('../utils/promise');
-var defaultBlocks = require('../constants/defaultBlocks');
-var fileToOutput = require('./helper/fileToOutput');
+const Modifiers = require('./modifiers');
+const resolveFileToURL = require('./helper/resolveFileToURL');
+const Api = require('../api');
+const Plugins = require('../plugins');
+const Promise = require('../utils/promise');
+const defaultBlocks = require('../constants/defaultBlocks');
+const fileToOutput = require('./helper/fileToOutput');
 
-var CODEBLOCK = 'code';
+const CODEBLOCK = 'code';
 
 /**
  * Return default modifier to prepare a page for
@@ -15,25 +15,25 @@ var CODEBLOCK = 'code';
  * @return {Array<Modifier>}
  */
 function getModifiers(output, page) {
-    var book = output.getBook();
-    var plugins = output.getPlugins();
-    var glossary = book.getGlossary();
-    var file = page.getFile();
+    const book = output.getBook();
+    const plugins = output.getPlugins();
+    const glossary = book.getGlossary();
+    const file = page.getFile();
 
     // Glossary entries
-    var entries = glossary.getEntries();
-    var glossaryFile = glossary.getFile();
-    var glossaryFilename = fileToOutput(output, glossaryFile.getPath());
+    const entries = glossary.getEntries();
+    const glossaryFile = glossary.getFile();
+    const glossaryFilename = fileToOutput(output, glossaryFile.getPath());
 
     // Current file path
-    var currentFilePath = file.getPath();
+    const currentFilePath = file.getPath();
 
     // Get TemplateBlock for highlighting
-    var blocks = Plugins.listBlocks(plugins);
-    var code = blocks.get(CODEBLOCK) || defaultBlocks.get(CODEBLOCK);
+    const blocks = Plugins.listBlocks(plugins);
+    const code = blocks.get(CODEBLOCK) || defaultBlocks.get(CODEBLOCK);
 
     // Current context
-    var context = Api.encodeGlobal(output);
+    const context = Api.encodeGlobal(output);
 
     return [
         // Normalize IDs on headings
diff --git a/packages/gitbook/lib/output/helper/fileToOutput.js b/packages/gitbook/src/output/helper/fileToOutput.js
index 361c6eb..a514854 100644
--- a/packages/gitbook/lib/output/helper/fileToOutput.js
+++ b/packages/gitbook/src/output/helper/fileToOutput.js
@@ -1,9 +1,9 @@
-var path = require('path');
+const path = require('path');
 
-var PathUtils = require('../../utils/path');
-var LocationUtils = require('../../utils/location');
+const PathUtils = require('../../utils/path');
+const LocationUtils = require('../../utils/location');
 
-var OUTPUT_EXTENSION = '.html';
+const OUTPUT_EXTENSION = '.html';
 
 /**
  * Convert a filePath (absolute) to a filename for output
@@ -13,9 +13,9 @@ var OUTPUT_EXTENSION = '.html';
  * @return {String}
  */
 function fileToOutput(output, filePath) {
-    var book = output.getBook();
-    var readme = book.getReadme();
-    var fileReadme = readme.getFile();
+    const book = output.getBook();
+    const readme = book.getReadme();
+    const fileReadme = readme.getFile();
 
     if (
         path.basename(filePath, path.extname(filePath)) == 'README' ||
diff --git a/packages/gitbook/lib/output/helper/fileToURL.js b/packages/gitbook/src/output/helper/fileToURL.js
index 44ad2d8..a42bca6 100644
--- a/packages/gitbook/lib/output/helper/fileToURL.js
+++ b/packages/gitbook/src/output/helper/fileToURL.js
@@ -1,7 +1,7 @@
-var path = require('path');
-var LocationUtils = require('../../utils/location');
+const path = require('path');
+const LocationUtils = require('../../utils/location');
 
-var fileToOutput = require('./fileToOutput');
+const fileToOutput = require('./fileToOutput');
 
 /**
     Convert a filePath (absolute) to an url (without hostname).
@@ -16,8 +16,8 @@ var fileToOutput = require('./fileToOutput');
     @return {String}
 */
 function fileToURL(output, filePath) {
-    var options = output.getOptions();
-    var directoryIndex = options.get('directoryIndex');
+    const options = output.getOptions();
+    const directoryIndex = options.get('directoryIndex');
 
     filePath = fileToOutput(output, filePath);
 
diff --git a/packages/gitbook/lib/output/helper/index.js b/packages/gitbook/src/output/helper/index.js
index f8bc109..f8bc109 100644
--- a/packages/gitbook/lib/output/helper/index.js
+++ b/packages/gitbook/src/output/helper/index.js
diff --git a/packages/gitbook/lib/output/helper/resolveFileToURL.js b/packages/gitbook/src/output/helper/resolveFileToURL.js
index 3f52713..907cfdd 100644
--- a/packages/gitbook/lib/output/helper/resolveFileToURL.js
+++ b/packages/gitbook/src/output/helper/resolveFileToURL.js
@@ -1,6 +1,6 @@
-var LocationUtils = require('../../utils/location');
+const LocationUtils = require('../../utils/location');
 
-var fileToURL = require('./fileToURL');
+const fileToURL = require('./fileToURL');
 
 /**
  * Resolve an absolute path (extracted from a link)
@@ -13,7 +13,7 @@ function resolveFileToURL(output, filePath) {
     // Convert /test.png -> test.png
     filePath = LocationUtils.toAbsolute(filePath, '', '');
 
-    var page = output.getPage(filePath);
+    const page = output.getPage(filePath);
 
     // if file is a page, return correct .html url
     if (page) {
diff --git a/packages/gitbook/lib/output/helper/writeFile.js b/packages/gitbook/src/output/helper/writeFile.js
index a6d4645..01a8e68 100644
--- a/packages/gitbook/lib/output/helper/writeFile.js
+++ b/packages/gitbook/src/output/helper/writeFile.js
@@ -1,5 +1,5 @@
-var path = require('path');
-var fs = require('../../utils/fs');
+const path = require('path');
+const fs = require('../../utils/fs');
 
 /**
     Write a file to the output folder
@@ -10,7 +10,7 @@ var fs = require('../../utils/fs');
     @return {Promise}
 */
 function writeFile(output, filePath, content) {
-    var rootFolder = output.getRoot();
+    const rootFolder = output.getRoot();
     filePath = path.join(rootFolder, filePath);
 
     return fs.ensureFile(filePath)
diff --git a/packages/gitbook/lib/output/index.js b/packages/gitbook/src/output/index.js
index 9b8ec17..574b3df 100644
--- a/packages/gitbook/lib/output/index.js
+++ b/packages/gitbook/src/output/index.js
@@ -1,6 +1,6 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var generators = Immutable.List([
+const generators = Immutable.List([
     require('./json'),
     require('./website'),
     require('./ebook')
@@ -20,5 +20,5 @@ function getGenerator(name) {
 
 module.exports = {
     generate:           require('./generateBook'),
-    getGenerator:       getGenerator
+    getGenerator
 };
diff --git a/packages/gitbook/lib/output/json/index.js b/packages/gitbook/src/output/json/index.js
index 361da06..361da06 100644
--- a/packages/gitbook/lib/output/json/index.js
+++ b/packages/gitbook/src/output/json/index.js
diff --git a/packages/gitbook/lib/output/json/onFinish.js b/packages/gitbook/src/output/json/onFinish.js
index d41d778..b05057a 100644
--- a/packages/gitbook/lib/output/json/onFinish.js
+++ b/packages/gitbook/src/output/json/onFinish.js
@@ -1,8 +1,8 @@
-var path = require('path');
+const path = require('path');
 
-var Promise = require('../../utils/promise');
-var fs = require('../../utils/fs');
-var JSONUtils = require('../../json');
+const Promise = require('../../utils/promise');
+const fs = require('../../utils/fs');
+const JSONUtils = require('../../json');
 
 /**
     Finish the generation
@@ -11,23 +11,23 @@ var JSONUtils = require('../../json');
     @return {Output}
 */
 function onFinish(output) {
-    var book = output.getBook();
-    var outputRoot = output.getRoot();
+    const book = output.getBook();
+    const outputRoot = output.getRoot();
 
     if (!book.isMultilingual()) {
         return Promise(output);
     }
 
     // Get main language
-    var languages = book.getLanguages();
-    var mainLanguage = languages.getDefaultLanguage();
+    const languages = book.getLanguages();
+    const mainLanguage = languages.getDefaultLanguage();
 
     // Read the main JSON
     return fs.readFile(path.resolve(outputRoot, mainLanguage.getID(), 'README.json'), 'utf8')
 
     // Extend the JSON
     .then(function(content) {
-        var json = JSON.parse(content);
+        const json = JSON.parse(content);
 
         json.languages = JSONUtils.encodeLanguages(languages);
 
diff --git a/packages/gitbook/lib/output/json/onPage.js b/packages/gitbook/src/output/json/onPage.js
index 2315ba0..8bee711 100644
--- a/packages/gitbook/lib/output/json/onPage.js
+++ b/packages/gitbook/src/output/json/onPage.js
@@ -1,10 +1,10 @@
-var JSONUtils = require('../../json');
-var PathUtils = require('../../utils/path');
-var Modifiers = require('../modifiers');
-var writeFile = require('../helper/writeFile');
-var getModifiers = require('../getModifiers');
+const JSONUtils = require('../../json');
+const PathUtils = require('../../utils/path');
+const Modifiers = require('../modifiers');
+const writeFile = require('../helper/writeFile');
+const getModifiers = require('../getModifiers');
 
-var JSON_VERSION = '3';
+const JSON_VERSION = '3';
 
 /**
  * Write a page as a json file
@@ -13,13 +13,13 @@ var JSON_VERSION = '3';
  * @param {Page} page
  */
 function onPage(output, page) {
-    var file = page.getFile();
-    var readme = output.getBook().getReadme().getFile();
+    const file = page.getFile();
+    const readme = output.getBook().getReadme().getFile();
 
     return Modifiers.modifyHTML(page, getModifiers(output, page))
     .then(function(resultPage) {
         // Generate the JSON
-        var json = JSONUtils.encodeBookWithPage(output.getBook(), resultPage);
+        const json = JSONUtils.encodeBookWithPage(output.getBook(), resultPage);
 
         // Delete some private properties
         delete json.config;
@@ -28,7 +28,7 @@ function onPage(output, page) {
         json.version = JSON_VERSION;
 
         // File path in the output folder
-        var filePath = file.getPath() == readme.getPath()? 'README.json' : file.getPath();
+        let filePath = file.getPath() == readme.getPath() ? 'README.json' : file.getPath();
         filePath = PathUtils.setExtension(filePath, '.json');
 
         // Write it to the disk
diff --git a/packages/gitbook/lib/output/json/options.js b/packages/gitbook/src/output/json/options.js
index 79167b1..2a9de0e 100644
--- a/packages/gitbook/lib/output/json/options.js
+++ b/packages/gitbook/src/output/json/options.js
@@ -1,6 +1,6 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var Options = Immutable.Record({
+const Options = Immutable.Record({
     // Root folder for the output
     root:       String()
 });
diff --git a/packages/gitbook/lib/output/modifiers/__tests__/addHeadingId.js b/packages/gitbook/src/output/modifiers/__tests__/addHeadingId.js
index a3b1d81..4d77e75 100644
--- a/packages/gitbook/lib/output/modifiers/__tests__/addHeadingId.js
+++ b/packages/gitbook/src/output/modifiers/__tests__/addHeadingId.js
@@ -1,26 +1,25 @@
-var cheerio = require('cheerio');
-var addHeadingId = require('../addHeadingId');
+const cheerio = require('cheerio');
+const addHeadingId = require('../addHeadingId');
 
 describe('addHeadingId', function() {
     it('should add an ID if none', function() {
-        var $ = cheerio.load('<h1>Hello World</h1><h2>Cool !!</h2>');
+        const $ = cheerio.load('<h1>Hello World</h1><h2>Cool !!</h2>');
 
         return addHeadingId($)
         .then(function() {
-            var html = $.html();
+            const html = $.html();
             expect(html).toBe('<h1 id="hello-world">Hello World</h1><h2 id="cool-">Cool !!</h2>');
         });
     });
 
     it('should not change existing IDs', function() {
-        var $ = cheerio.load('<h1 id="awesome">Hello World</h1>');
+        const $ = cheerio.load('<h1 id="awesome">Hello World</h1>');
 
         return addHeadingId($)
         .then(function() {
-            var html = $.html();
+            const html = $.html();
             expect(html).toBe('<h1 id="awesome">Hello World</h1>');
         });
     });
 });
 
-
diff --git a/packages/gitbook/lib/output/modifiers/__tests__/annotateText.js b/packages/gitbook/src/output/modifiers/__tests__/annotateText.js
index 67e7a10..28a5cc5 100644
--- a/packages/gitbook/lib/output/modifiers/__tests__/annotateText.js
+++ b/packages/gitbook/src/output/modifiers/__tests__/annotateText.js
@@ -1,46 +1,45 @@
-var Immutable = require('immutable');
-var cheerio = require('cheerio');
-var GlossaryEntry = require('../../../models/glossaryEntry');
-var annotateText = require('../annotateText');
+const Immutable = require('immutable');
+const cheerio = require('cheerio');
+const GlossaryEntry = require('../../../models/glossaryEntry');
+const annotateText = require('../annotateText');
 
 describe('annotateText', function() {
-    var entries = Immutable.List([
+    const entries = Immutable.List([
         GlossaryEntry({ name: 'Word' }),
         GlossaryEntry({ name: 'Multiple Words' })
     ]);
 
     it('should annotate text', function() {
-        var $ = cheerio.load('<p>This is a word, and multiple words</p>');
+        const $ = cheerio.load('<p>This is a word, and multiple words</p>');
 
         annotateText(entries, 'GLOSSARY.md', $);
 
-        var links = $('a');
+        const links = $('a');
         expect(links.length).toBe(2);
 
-        var word = $(links.get(0));
+        const word = $(links.get(0));
         expect(word.attr('href')).toBe('/GLOSSARY.md#word');
         expect(word.text()).toBe('word');
         expect(word.hasClass('glossary-term')).toBeTruthy();
 
-        var words = $(links.get(1));
+        const words = $(links.get(1));
         expect(words.attr('href')).toBe('/GLOSSARY.md#multiple-words');
         expect(words.text()).toBe('multiple words');
         expect(words.hasClass('glossary-term')).toBeTruthy();
     });
 
     it('should not annotate scripts', function() {
-        var $ = cheerio.load('<script>This is a word, and multiple words</script>');
+        const $ = cheerio.load('<script>This is a word, and multiple words</script>');
 
         annotateText(entries, 'GLOSSARY.md', $);
         expect($('a').length).toBe(0);
     });
 
     it('should not annotate when has class "no-glossary"', function() {
-        var $ = cheerio.load('<p class="no-glossary">This is a word, and multiple words</p>');
+        const $ = cheerio.load('<p class="no-glossary">This is a word, and multiple words</p>');
 
         annotateText(entries, 'GLOSSARY.md', $);
         expect($('a').length).toBe(0);
     });
 });
 
-
diff --git a/packages/gitbook/src/output/modifiers/__tests__/fetchRemoteImages.js b/packages/gitbook/src/output/modifiers/__tests__/fetchRemoteImages.js
new file mode 100644
index 0000000..9145cae
--- /dev/null
+++ b/packages/gitbook/src/output/modifiers/__tests__/fetchRemoteImages.js
@@ -0,0 +1,39 @@
+const cheerio = require('cheerio');
+const tmp = require('tmp');
+const path = require('path');
+
+const URL = 'https://upload.wikimedia.org/wikipedia/commons/thumb/4/47/PNG_transparency_demonstration_1.png/280px-PNG_transparency_demonstration_1.png';
+
+describe('fetchRemoteImages', function() {
+    let dir;
+    const fetchRemoteImages = require('../fetchRemoteImages');
+
+    beforeEach(function() {
+        dir = tmp.dirSync();
+    });
+
+    it('should download image file', function() {
+        const $ = cheerio.load('<img src="' + URL + '" />');
+
+        return fetchRemoteImages(dir.name, 'index.html', $)
+        .then(function() {
+            const $img = $('img');
+            const src = $img.attr('src');
+
+            expect(dir.name).toHaveFile(src);
+        });
+    });
+
+    it('should download image file and replace with relative path', function() {
+        const $ = cheerio.load('<img src="' + URL + '" />');
+
+        return fetchRemoteImages(dir.name, 'test/index.html', $)
+        .then(function() {
+            const $img = $('img');
+            const src = $img.attr('src');
+
+            expect(dir.name).toHaveFile(path.join('test', src));
+        });
+    });
+});
+
diff --git a/packages/gitbook/lib/output/modifiers/__tests__/highlightCode.js b/packages/gitbook/src/output/modifiers/__tests__/highlightCode.js
index 75d9902..d93417b 100644
--- a/packages/gitbook/lib/output/modifiers/__tests__/highlightCode.js
+++ b/packages/gitbook/src/output/modifiers/__tests__/highlightCode.js
@@ -1,6 +1,6 @@
-var cheerio = require('cheerio');
-var Promise = require('../../../utils/promise');
-var highlightCode = require('../highlightCode');
+const cheerio = require('cheerio');
+const Promise = require('../../../utils/promise');
+const highlightCode = require('../highlightCode');
 
 describe('highlightCode', function() {
     function doHighlight(lang, code) {
@@ -17,44 +17,43 @@ describe('highlightCode', function() {
     }
 
     it('should call it for normal code element', function() {
-        var $ = cheerio.load('<p>This is a <code>test</code></p>');
+        const $ = cheerio.load('<p>This is a <code>test</code></p>');
 
         return highlightCode(doHighlight, $)
         .then(function() {
-            var $code = $('code');
+            const $code = $('code');
             expect($code.text()).toBe('$test');
         });
     });
 
     it('should call it for markdown code block', function() {
-        var $ = cheerio.load('<pre><code class="lang-js">test</code></pre>');
+        const $ = cheerio.load('<pre><code class="lang-js">test</code></pre>');
 
         return highlightCode(doHighlight, $)
         .then(function() {
-            var $code = $('code');
+            const $code = $('code');
             expect($code.text()).toBe('js$test');
         });
     });
 
     it('should call it for asciidoc code block', function() {
-        var $ = cheerio.load('<pre><code class="language-python">test</code></pre>');
+        const $ = cheerio.load('<pre><code class="language-python">test</code></pre>');
 
         return highlightCode(doHighlight, $)
         .then(function() {
-            var $code = $('code');
+            const $code = $('code');
             expect($code.text()).toBe('python$test');
         });
     });
 
     it('should accept async highlighter', function() {
-        var $ = cheerio.load('<pre><code class="language-python">test</code></pre>');
+        const $ = cheerio.load('<pre><code class="language-python">test</code></pre>');
 
         return highlightCode(doHighlightAsync, $)
         .then(function() {
-            var $code = $('code');
+            const $code = $('code');
             expect($code.text()).toBe('python$test');
         });
     });
 });
 
-
diff --git a/packages/gitbook/src/output/modifiers/__tests__/inlinePng.js b/packages/gitbook/src/output/modifiers/__tests__/inlinePng.js
new file mode 100644
index 0000000..fd031b0
--- /dev/null
+++ b/packages/gitbook/src/output/modifiers/__tests__/inlinePng.js
@@ -0,0 +1,24 @@
+const cheerio = require('cheerio');
+const tmp = require('tmp');
+const inlinePng = require('../inlinePng');
+
+describe('inlinePng', function() {
+    let dir;
+
+    beforeEach(function() {
+        dir = tmp.dirSync();
+    });
+
+    it('should write an inline PNG using data URI as a file', function() {
+        const $ = cheerio.load('<img alt="GitBook Logo 20x20" src="data:image/png;base64,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"/>');
+
+        return inlinePng(dir.name, 'index.html', $)
+        .then(function() {
+            const $img = $('img');
+            const src = $img.attr('src');
+
+            expect(dir.name).toHaveFile(src);
+        });
+    });
+});
+
diff --git a/packages/gitbook/lib/output/modifiers/__tests__/resolveLinks.js b/packages/gitbook/src/output/modifiers/__tests__/resolveLinks.js
index 8904c11..167af5d 100644
--- a/packages/gitbook/lib/output/modifiers/__tests__/resolveLinks.js
+++ b/packages/gitbook/src/output/modifiers/__tests__/resolveLinks.js
@@ -1,6 +1,6 @@
-var path = require('path');
-var cheerio = require('cheerio');
-var resolveLinks = require('../resolveLinks');
+const path = require('path');
+const cheerio = require('cheerio');
+const resolveLinks = require('../resolveLinks');
 
 describe('resolveLinks', function() {
     function resolveFileBasic(href) {
@@ -16,24 +16,24 @@ describe('resolveLinks', function() {
     }
 
     describe('Absolute path', function() {
-        var TEST = '<p>This is a <a href="/test/cool.md"></a></p>';
+        const TEST = '<p>This is a <a href="/test/cool.md"></a></p>';
 
         it('should resolve path starting by "/" in root directory', function() {
-            var $ = cheerio.load(TEST);
+            const $ = cheerio.load(TEST);
 
             return resolveLinks('hello.md', resolveFileBasic, $)
             .then(function() {
-                var link = $('a');
+                const link = $('a');
                 expect(link.attr('href')).toBe('fakeDir/test/cool.md');
             });
         });
 
         it('should resolve path starting by "/" in child directory', function() {
-            var $ = cheerio.load(TEST);
+            const $ = cheerio.load(TEST);
 
             return resolveLinks('afolder/hello.md', resolveFileBasic, $)
             .then(function() {
-                var link = $('a');
+                const link = $('a');
                 expect(link.attr('href')).toBe('../fakeDir/test/cool.md');
             });
         });
@@ -41,61 +41,61 @@ describe('resolveLinks', function() {
 
     describe('Anchor', function() {
         it('should prevent anchors in resolution', function() {
-            var TEST = '<p>This is a <a href="test/cool.md#an-anchor"></a></p>';
-            var $ = cheerio.load(TEST);
+            const TEST = '<p>This is a <a href="test/cool.md#an-anchor"></a></p>';
+            const $ = cheerio.load(TEST);
 
             return resolveLinks('hello.md', resolveFileCustom, $)
             .then(function() {
-                var link = $('a');
+                const link = $('a');
                 expect(link.attr('href')).toBe('test/cool.html#an-anchor');
             });
         });
 
         it('should ignore pure anchor links', function() {
-            var TEST = '<p>This is a <a href="#an-anchor"></a></p>';
-            var $ = cheerio.load(TEST);
+            const TEST = '<p>This is a <a href="#an-anchor"></a></p>';
+            const $ = cheerio.load(TEST);
 
             return resolveLinks('hello.md', resolveFileCustom, $)
             .then(function() {
-                var link = $('a');
+                const link = $('a');
                 expect(link.attr('href')).toBe('#an-anchor');
             });
         });
     });
 
     describe('Custom Resolver', function() {
-        var TEST = '<p>This is a <a href="/test/cool.md"></a> <a href="afile.png"></a></p>';
+        const TEST = '<p>This is a <a href="/test/cool.md"></a> <a href="afile.png"></a></p>';
 
         it('should resolve path correctly for absolute path', function() {
-            var $ = cheerio.load(TEST);
+            const $ = cheerio.load(TEST);
 
             return resolveLinks('hello.md', resolveFileCustom, $)
             .then(function() {
-                var link = $('a').first();
+                const link = $('a').first();
                 expect(link.attr('href')).toBe('test/cool.html');
             });
         });
 
         it('should resolve path correctly for absolute path (2)', function() {
-            var $ = cheerio.load(TEST);
+            const $ = cheerio.load(TEST);
 
             return resolveLinks('afodler/hello.md', resolveFileCustom, $)
             .then(function() {
-                var link = $('a').first();
+                const link = $('a').first();
                 expect(link.attr('href')).toBe('../test/cool.html');
             });
         });
     });
 
     describe('External link', function() {
-        var TEST = '<p>This is a <a href="http://www.github.com">external link</a></p>';
+        const TEST = '<p>This is a <a href="http://www.github.com">external link</a></p>';
 
         it('should have target="_blank" attribute', function() {
-            var $ = cheerio.load(TEST);
+            const $ = cheerio.load(TEST);
 
             return resolveLinks('hello.md', resolveFileBasic, $)
             .then(function() {
-                var link = $('a');
+                const link = $('a');
                 expect(link.attr('target')).toBe('_blank');
             });
         });
diff --git a/packages/gitbook/src/output/modifiers/__tests__/svgToImg.js b/packages/gitbook/src/output/modifiers/__tests__/svgToImg.js
new file mode 100644
index 0000000..4bdab59
--- /dev/null
+++ b/packages/gitbook/src/output/modifiers/__tests__/svgToImg.js
@@ -0,0 +1,24 @@
+const cheerio = require('cheerio');
+const tmp = require('tmp');
+
+describe('svgToImg', function() {
+    let dir;
+    const svgToImg = require('../svgToImg');
+
+    beforeEach(function() {
+        dir = tmp.dirSync();
+    });
+
+    it('should write svg as a file', function() {
+        const $ = cheerio.load('<svg xmlns="http://www.w3.org/2000/svg" width="200" height="100" version="1.1"><rect width="200" height="100" stroke="black" stroke-width="6" fill="green"/></svg>');
+
+        return svgToImg(dir.name, 'index.html', $)
+        .then(function() {
+            const $img = $('img');
+            const src = $img.attr('src');
+
+            expect(dir.name).toHaveFile(src);
+        });
+    });
+});
+
diff --git a/packages/gitbook/src/output/modifiers/__tests__/svgToPng.js b/packages/gitbook/src/output/modifiers/__tests__/svgToPng.js
new file mode 100644
index 0000000..0a12938
--- /dev/null
+++ b/packages/gitbook/src/output/modifiers/__tests__/svgToPng.js
@@ -0,0 +1,32 @@
+const cheerio = require('cheerio');
+const tmp = require('tmp');
+const path = require('path');
+
+const svgToImg = require('../svgToImg');
+const svgToPng = require('../svgToPng');
+
+describe('svgToPng', function() {
+    let dir;
+
+    beforeEach(function() {
+        dir = tmp.dirSync();
+    });
+
+    it('should write svg as png file', function() {
+        const $ = cheerio.load('<svg xmlns="http://www.w3.org/2000/svg" width="200" height="100" version="1.1"><rect width="200" height="100" stroke="black" stroke-width="6" fill="green"/></svg>');
+        const fileName = 'index.html';
+
+        return svgToImg(dir.name, fileName, $)
+        .then(function() {
+            return svgToPng(dir.name, fileName, $);
+        })
+        .then(function() {
+            const $img = $('img');
+            const src = $img.attr('src');
+
+            expect(dir.name).toHaveFile(src);
+            expect(path.extname(src)).toBe('.png');
+        });
+    });
+});
+
diff --git a/packages/gitbook/lib/output/modifiers/addHeadingId.js b/packages/gitbook/src/output/modifiers/addHeadingId.js
index e2e2720..e5bab3e 100644
--- a/packages/gitbook/lib/output/modifiers/addHeadingId.js
+++ b/packages/gitbook/src/output/modifiers/addHeadingId.js
@@ -1,5 +1,5 @@
-var slug = require('github-slugid');
-var editHTMLElement = require('./editHTMLElement');
+const slug = require('github-slugid');
+const editHTMLElement = require('./editHTMLElement');
 
 /**
     Add ID to an heading
diff --git a/packages/gitbook/lib/output/modifiers/annotateText.js b/packages/gitbook/src/output/modifiers/annotateText.js
index 490c228..36ee4e9 100644
--- a/packages/gitbook/lib/output/modifiers/annotateText.js
+++ b/packages/gitbook/src/output/modifiers/annotateText.js
@@ -1,46 +1,43 @@
-var escape = require('escape-html');
+const escape = require('escape-html');
 
 // Selector to ignore
-var ANNOTATION_IGNORE = '.no-glossary,code,pre,a,script,h1,h2,h3,h4,h5,h6';
+const ANNOTATION_IGNORE = '.no-glossary,code,pre,a,script,h1,h2,h3,h4,h5,h6';
 
-function pregQuote( str ) {
-    return (str+'').replace(/([\\\.\+\*\?\[\^\]\$\(\)\{\}\=\!\<\>\|\:])/g, '\\$1');
+function pregQuote(str) {
+    return (str + '').replace(/([\\\.\+\*\?\[\^\]\$\(\)\{\}\=\!\<\>\|\:])/g, '\\$1');
 }
 
-function replaceText($, el, search, replace, text_only ) {
-    return $(el).each(function(){
-        var node = this.firstChild,
-            val,
-            new_val,
-
-            // Elements to be removed at the end.
-            remove = [];
+function replaceText($, el, search, replace, text_only) {
+    return $(el).each(function() {
+        let node = this.firstChild, val, new_val;
+        // Elements to be removed at the end.
+        const remove = [];
 
         // Only continue if firstChild exists.
-        if ( node ) {
+        if (node) {
 
             // Loop over all childNodes.
             while (node) {
 
                 // Only process text nodes.
-                if ( node.nodeType === 3 ) {
+                if (node.nodeType === 3) {
 
                     // The original node value.
                     val = node.nodeValue;
 
                     // The new value.
-                    new_val = val.replace( search, replace );
+                    new_val = val.replace(search, replace);
 
                     // Only replace text if the new value is actually different!
-                    if ( new_val !== val ) {
+                    if (new_val !== val) {
 
-                        if ( !text_only && /</.test( new_val ) ) {
+                        if (!text_only && /</.test(new_val)) {
                             // The new value contains HTML, set it in a slower but far more
                             // robust way.
-                            $(node).before( new_val );
+                            $(node).before(new_val);
 
                             // Don't remove the node yet, or the loop will lose its place.
-                            remove.push( node );
+                            remove.push(node);
                         } else {
                             // The new value contains no HTML, so it can be set in this
                             // very fast, simple way.
@@ -67,13 +64,13 @@ function replaceText($, el, search, replace, text_only ) {
  */
 function annotateText(entries, glossaryFilePath, $) {
     entries.forEach(function(entry) {
-        var entryId     = entry.getID();
-        var name        = entry.getName();
-        var description = entry.getDescription();
-        var searchRegex = new RegExp( '\\b(' + pregQuote(name.toLowerCase()) + ')\\b' , 'gi' );
+        const entryId     = entry.getID();
+        const name        = entry.getName();
+        const description = entry.getDescription();
+        const searchRegex = new RegExp('\\b(' + pregQuote(name.toLowerCase()) + ')\\b' , 'gi');
 
         $('*').each(function() {
-            var $this = $(this);
+            const $this = $(this);
 
             if (
                 $this.is(ANNOTATION_IGNORE) ||
diff --git a/packages/gitbook/lib/output/modifiers/editHTMLElement.js b/packages/gitbook/src/output/modifiers/editHTMLElement.js
index 755598e..d0d2b19 100644
--- a/packages/gitbook/lib/output/modifiers/editHTMLElement.js
+++ b/packages/gitbook/src/output/modifiers/editHTMLElement.js
@@ -1,13 +1,13 @@
-var Promise = require('../../utils/promise');
+const Promise = require('../../utils/promise');
 
 /**
     Edit all elements matching a selector
 */
 function editHTMLElement($, selector, fn) {
-    var $elements = $(selector);
+    const $elements = $(selector);
 
     return Promise.forEach($elements, function(el) {
-        var $el = $(el);
+        const $el = $(el);
         return fn($el);
     });
 }
diff --git a/packages/gitbook/lib/output/modifiers/fetchRemoteImages.js b/packages/gitbook/src/output/modifiers/fetchRemoteImages.js
index ef868b9..1732247 100644
--- a/packages/gitbook/lib/output/modifiers/fetchRemoteImages.js
+++ b/packages/gitbook/src/output/modifiers/fetchRemoteImages.js
@@ -1,9 +1,9 @@
-var path = require('path');
-var crc = require('crc');
+const path = require('path');
+const crc = require('crc');
 
-var editHTMLElement = require('./editHTMLElement');
-var fs = require('../../utils/fs');
-var LocationUtils = require('../../utils/location');
+const editHTMLElement = require('./editHTMLElement');
+const fs = require('../../utils/fs');
+const LocationUtils = require('../../utils/location');
 
 /**
     Fetch all remote images
@@ -14,20 +14,20 @@ var LocationUtils = require('../../utils/location');
     @return {Promise}
 */
 function fetchRemoteImages(rootFolder, currentFile, $) {
-    var currentDirectory = path.dirname(currentFile);
+    const currentDirectory = path.dirname(currentFile);
 
     return editHTMLElement($, 'img', function($img) {
-        var src = $img.attr('src');
-        var extension = path.extname(src);
+        let src = $img.attr('src');
+        const extension = path.extname(src);
 
         if (!LocationUtils.isExternal(src)) {
             return;
         }
 
         // We avoid generating twice the same PNG
-        var hash = crc.crc32(src).toString(16);
-        var fileName = hash + extension;
-        var filePath = path.join(rootFolder, fileName);
+        const hash = crc.crc32(src).toString(16);
+        const fileName = hash + extension;
+        const filePath = path.join(rootFolder, fileName);
 
         return fs.assertFile(filePath, function() {
             return fs.download(src, filePath);
diff --git a/packages/gitbook/lib/output/modifiers/highlightCode.js b/packages/gitbook/src/output/modifiers/highlightCode.js
index 5d397bb..622432d 100644
--- a/packages/gitbook/lib/output/modifiers/highlightCode.js
+++ b/packages/gitbook/src/output/modifiers/highlightCode.js
@@ -1,8 +1,8 @@
-var is = require('is');
-var Immutable = require('immutable');
+const is = require('is');
+const Immutable = require('immutable');
 
-var Promise = require('../../utils/promise');
-var editHTMLElement = require('./editHTMLElement');
+const Promise = require('../../utils/promise');
+const editHTMLElement = require('./editHTMLElement');
 
 /**
     Return language for a code blocks from a list of class names
@@ -40,9 +40,9 @@ function getLanguageForClass(classNames) {
 */
 function highlightCode(highlight, $) {
     return editHTMLElement($, 'code', function($code) {
-        var classNames = ($code.attr('class') || '').split(' ');
-        var lang = getLanguageForClass(classNames);
-        var source = $code.text();
+        const classNames = ($code.attr('class') || '').split(' ');
+        const lang = getLanguageForClass(classNames);
+        const source = $code.text();
 
         return Promise(highlight(lang, source))
         .then(function(r) {
diff --git a/packages/gitbook/lib/output/modifiers/index.js b/packages/gitbook/src/output/modifiers/index.js
index f1daa2b..f1daa2b 100644
--- a/packages/gitbook/lib/output/modifiers/index.js
+++ b/packages/gitbook/src/output/modifiers/index.js
diff --git a/packages/gitbook/lib/output/modifiers/inlineAssets.js b/packages/gitbook/src/output/modifiers/inlineAssets.js
index 7cd874b..1ed4344 100644
--- a/packages/gitbook/lib/output/modifiers/inlineAssets.js
+++ b/packages/gitbook/src/output/modifiers/inlineAssets.js
@@ -1,10 +1,10 @@
-var svgToImg = require('./svgToImg');
-var svgToPng = require('./svgToPng');
-var inlinePng = require('./inlinePng');
-var resolveImages = require('./resolveImages');
-var fetchRemoteImages = require('./fetchRemoteImages');
+const svgToImg = require('./svgToImg');
+const svgToPng = require('./svgToPng');
+const inlinePng = require('./inlinePng');
+const resolveImages = require('./resolveImages');
+const fetchRemoteImages = require('./fetchRemoteImages');
 
-var Promise = require('../../utils/promise');
+const Promise = require('../../utils/promise');
 
 /**
     Inline all assets in a page
diff --git a/packages/gitbook/lib/output/modifiers/inlinePng.js b/packages/gitbook/src/output/modifiers/inlinePng.js
index 161f164..218aaa2 100644
--- a/packages/gitbook/lib/output/modifiers/inlinePng.js
+++ b/packages/gitbook/src/output/modifiers/inlinePng.js
@@ -1,11 +1,11 @@
-var crc = require('crc');
-var path = require('path');
+const crc = require('crc');
+const path = require('path');
 
-var imagesUtil = require('../../utils/images');
-var fs = require('../../utils/fs');
-var LocationUtils = require('../../utils/location');
+const imagesUtil = require('../../utils/images');
+const fs = require('../../utils/fs');
+const LocationUtils = require('../../utils/location');
 
-var editHTMLElement = require('./editHTMLElement');
+const editHTMLElement = require('./editHTMLElement');
 
 /**
     Convert all inline PNG images to PNG file
@@ -15,20 +15,20 @@ var editHTMLElement = require('./editHTMLElement');
     @return {Promise}
 */
 function inlinePng(rootFolder, currentFile, $) {
-    var currentDirectory = path.dirname(currentFile);
+    const currentDirectory = path.dirname(currentFile);
 
     return editHTMLElement($, 'img', function($img) {
-        var src = $img.attr('src');
+        const src = $img.attr('src');
         if (!LocationUtils.isDataURI(src)) {
             return;
         }
 
         // We avoid generating twice the same PNG
-        var hash = crc.crc32(src).toString(16);
-        var fileName = hash + '.png';
+        const hash = crc.crc32(src).toString(16);
+        let fileName = hash + '.png';
 
         // Result file path
-        var filePath = path.join(rootFolder, fileName);
+        const filePath = path.join(rootFolder, fileName);
 
         return fs.assertFile(filePath, function() {
             return imagesUtil.convertInlinePNG(src, filePath);
diff --git a/packages/gitbook/lib/output/modifiers/modifyHTML.js b/packages/gitbook/src/output/modifiers/modifyHTML.js
index cd3d6e5..00177fc 100644
--- a/packages/gitbook/lib/output/modifiers/modifyHTML.js
+++ b/packages/gitbook/src/output/modifiers/modifyHTML.js
@@ -1,5 +1,5 @@
-var cheerio = require('cheerio');
-var Promise = require('../../utils/promise');
+const cheerio = require('cheerio');
+const Promise = require('../../utils/promise');
 
 /**
     Apply a list of operations to a page and
@@ -10,14 +10,14 @@ var Promise = require('../../utils/promise');
     @return {Promise<Page>}
 */
 function modifyHTML(page, operations) {
-    var html = page.getContent();
-    var $ = cheerio.load(html);
+    const html = page.getContent();
+    const $ = cheerio.load(html);
 
     return Promise.forEach(operations, function(op) {
         return op($);
     })
     .then(function() {
-        var resultHTML = $.html();
+        const resultHTML = $.html();
         return page.set('content', resultHTML);
     });
 }
diff --git a/packages/gitbook/lib/output/modifiers/resolveImages.js b/packages/gitbook/src/output/modifiers/resolveImages.js
index cc25cfa..339ddeb 100644
--- a/packages/gitbook/lib/output/modifiers/resolveImages.js
+++ b/packages/gitbook/src/output/modifiers/resolveImages.js
@@ -1,7 +1,7 @@
-var path = require('path');
+const path = require('path');
 
-var LocationUtils = require('../../utils/location');
-var editHTMLElement = require('./editHTMLElement');
+const LocationUtils = require('../../utils/location');
+const editHTMLElement = require('./editHTMLElement');
 
 /**
     Resolve all HTML images:
@@ -11,10 +11,10 @@ var editHTMLElement = require('./editHTMLElement');
     @param {HTMLDom} $
 */
 function resolveImages(currentFile, $) {
-    var currentDirectory = path.dirname(currentFile);
+    const currentDirectory = path.dirname(currentFile);
 
     return editHTMLElement($, 'img', function($img) {
-        var src = $img.attr('src');
+        let src = $img.attr('src');
 
         if (LocationUtils.isExternal(src) || LocationUtils.isDataURI(src)) {
             return;
diff --git a/packages/gitbook/lib/output/modifiers/resolveLinks.js b/packages/gitbook/src/output/modifiers/resolveLinks.js
index 9d15e5e..8b15315 100644
--- a/packages/gitbook/lib/output/modifiers/resolveLinks.js
+++ b/packages/gitbook/src/output/modifiers/resolveLinks.js
@@ -1,8 +1,8 @@
-var path = require('path');
-var url = require('url');
+const path = require('path');
+const url = require('url');
 
-var LocationUtils = require('../../utils/location');
-var editHTMLElement = require('./editHTMLElement');
+const LocationUtils = require('../../utils/location');
+const editHTMLElement = require('./editHTMLElement');
 
 /**
     Resolve all HTML links:
@@ -13,10 +13,10 @@ var editHTMLElement = require('./editHTMLElement');
     @param {HTMLDom} $
 */
 function resolveLinks(currentFile, resolveFile, $) {
-    var currentDirectory = path.dirname(currentFile);
+    const currentDirectory = path.dirname(currentFile);
 
     return editHTMLElement($, 'a', function($a) {
-        var href = $a.attr('href');
+        let href = $a.attr('href');
 
         // Don't change a tag without href
         if (!href) {
@@ -29,7 +29,7 @@ function resolveLinks(currentFile, resolveFile, $) {
         }
 
         // Split anchor
-        var parsed = url.parse(href);
+        const parsed = url.parse(href);
         href = parsed.pathname || '';
 
         if (href) {
diff --git a/packages/gitbook/lib/output/modifiers/svgToImg.js b/packages/gitbook/src/output/modifiers/svgToImg.js
index f31b06d..ac37d07 100644
--- a/packages/gitbook/lib/output/modifiers/svgToImg.js
+++ b/packages/gitbook/src/output/modifiers/svgToImg.js
@@ -1,10 +1,10 @@
-var path = require('path');
-var crc = require('crc');
-var domSerializer = require('dom-serializer');
+const path = require('path');
+const crc = require('crc');
+const domSerializer = require('dom-serializer');
 
-var editHTMLElement = require('./editHTMLElement');
-var fs = require('../../utils/fs');
-var LocationUtils = require('../../utils/location');
+const editHTMLElement = require('./editHTMLElement');
+const fs = require('../../utils/fs');
+const LocationUtils = require('../../utils/location');
 
 /**
     Render a cheerio DOM as html
@@ -18,7 +18,7 @@ function renderDOM($, dom, options) {
     if (!dom && $._root && $._root.children) {
         dom = $._root.children;
     }
-    options = options|| dom.options || $._options;
+    options = options || dom.options || $._options;
     return domSerializer(dom, options);
 }
 
@@ -29,16 +29,16 @@ function renderDOM($, dom, options) {
     @param {HTMLDom} $
 */
 function svgToImg(baseFolder, currentFile, $) {
-    var currentDirectory = path.dirname(currentFile);
+    const currentDirectory = path.dirname(currentFile);
 
     return editHTMLElement($, 'svg', function($svg) {
-        var content = '<?xml version="1.0" encoding="UTF-8"?>' +
+        const content = '<?xml version="1.0" encoding="UTF-8"?>' +
             renderDOM($, $svg);
 
         // We avoid generating twice the same PNG
-        var hash = crc.crc32(content).toString(16);
-        var fileName = hash + '.svg';
-        var filePath = path.join(baseFolder, fileName);
+        const hash = crc.crc32(content).toString(16);
+        const fileName = hash + '.svg';
+        const filePath = path.join(baseFolder, fileName);
 
         // Write the svg to the file
         return fs.assertFile(filePath, function() {
@@ -47,7 +47,7 @@ function svgToImg(baseFolder, currentFile, $) {
 
         // Return as image
         .then(function() {
-            var src = LocationUtils.relative(currentDirectory, fileName);
+            const src = LocationUtils.relative(currentDirectory, fileName);
             $svg.replaceWith('<img src="' + src + '" />');
         });
     });
diff --git a/packages/gitbook/lib/output/modifiers/svgToPng.js b/packages/gitbook/src/output/modifiers/svgToPng.js
index 1093106..ad3f31f 100644
--- a/packages/gitbook/lib/output/modifiers/svgToPng.js
+++ b/packages/gitbook/src/output/modifiers/svgToPng.js
@@ -1,11 +1,11 @@
-var crc = require('crc');
-var path = require('path');
+const crc = require('crc');
+const path = require('path');
 
-var imagesUtil = require('../../utils/images');
-var fs = require('../../utils/fs');
-var LocationUtils = require('../../utils/location');
+const imagesUtil = require('../../utils/images');
+const fs = require('../../utils/fs');
+const LocationUtils = require('../../utils/location');
 
-var editHTMLElement = require('./editHTMLElement');
+const editHTMLElement = require('./editHTMLElement');
 
 /**
     Convert all SVG images to PNG
@@ -15,10 +15,10 @@ var editHTMLElement = require('./editHTMLElement');
     @return {Promise}
 */
 function svgToPng(rootFolder, currentFile, $) {
-    var currentDirectory = path.dirname(currentFile);
+    const currentDirectory = path.dirname(currentFile);
 
     return editHTMLElement($, 'img', function($img) {
-        var src = $img.attr('src');
+        let src = $img.attr('src');
         if (path.extname(src) !== '.svg') {
             return;
         }
@@ -27,14 +27,14 @@ function svgToPng(rootFolder, currentFile, $) {
         src = LocationUtils.toAbsolute(src, currentDirectory, '.');
 
         // We avoid generating twice the same PNG
-        var hash = crc.crc32(src).toString(16);
-        var fileName = hash + '.png';
+        const hash = crc.crc32(src).toString(16);
+        let fileName = hash + '.png';
 
         // Input file path
-        var inputPath = path.join(rootFolder, src);
+        const inputPath = path.join(rootFolder, src);
 
         // Result file path
-        var filePath = path.join(rootFolder, fileName);
+        const filePath = path.join(rootFolder, fileName);
 
         return fs.assertFile(filePath, function() {
             return imagesUtil.convertSVGToPNG(inputPath, filePath);
diff --git a/packages/gitbook/lib/output/prepareAssets.js b/packages/gitbook/src/output/prepareAssets.js
index ae9b55a..6694a74 100644
--- a/packages/gitbook/lib/output/prepareAssets.js
+++ b/packages/gitbook/src/output/prepareAssets.js
@@ -1,4 +1,4 @@
-var Parse = require('../parse');
+const Parse = require('../parse');
 
 /**
     List all assets in the book
@@ -7,9 +7,9 @@ var Parse = require('../parse');
     @return {Promise<Output>}
 */
 function prepareAssets(output) {
-    var book = output.getBook();
-    var pages = output.getPages();
-    var logger = output.getLogger();
+    const book = output.getBook();
+    const pages = output.getPages();
+    const logger = output.getLogger();
 
     return Parse.listAssets(book, pages)
     .then(function(assets) {
diff --git a/packages/gitbook/lib/output/preparePages.js b/packages/gitbook/src/output/preparePages.js
index 83944ed..e65367e 100644
--- a/packages/gitbook/lib/output/preparePages.js
+++ b/packages/gitbook/src/output/preparePages.js
@@ -1,5 +1,5 @@
-var Parse = require('../parse');
-var Promise = require('../utils/promise');
+const Parse = require('../parse');
+const Promise = require('../utils/promise');
 
 /**
     List and prepare all pages
@@ -8,8 +8,8 @@ var Promise = require('../utils/promise');
     @return {Promise<Output>}
 */
 function preparePages(output) {
-    var book = output.getBook();
-    var logger = book.getLogger();
+    const book = output.getBook();
+    const logger = book.getLogger();
 
     if (book.isMultilingual()) {
         return Promise(output);
diff --git a/packages/gitbook/lib/output/preparePlugins.js b/packages/gitbook/src/output/preparePlugins.js
index 5c4be93..c84bade 100644
--- a/packages/gitbook/lib/output/preparePlugins.js
+++ b/packages/gitbook/src/output/preparePlugins.js
@@ -1,5 +1,5 @@
-var Plugins = require('../plugins');
-var Promise = require('../utils/promise');
+const Plugins = require('../plugins');
+const Promise = require('../utils/promise');
 
 /**
  * Load and setup plugins
@@ -8,7 +8,7 @@ var Promise = require('../utils/promise');
  * @return {Promise<Output>}
  */
 function preparePlugins(output) {
-    var book = output.getBook();
+    const book = output.getBook();
 
     return Promise()
 
@@ -27,7 +27,7 @@ function preparePlugins(output) {
         .then(function(newBook) {
             return output.merge({
                 book: newBook,
-                plugins: plugins
+                plugins
             });
         });
     });
diff --git a/packages/gitbook/lib/output/website/__tests__/i18n.js b/packages/gitbook/src/output/website/__tests__/i18n.js
index fd610fb..24f01f3 100644
--- a/packages/gitbook/lib/output/website/__tests__/i18n.js
+++ b/packages/gitbook/src/output/website/__tests__/i18n.js
@@ -1,8 +1,8 @@
-var createMockOutput = require('../../__tests__/createMock');
-var prepareI18n = require('../prepareI18n');
-var createTemplateEngine = require('../createTemplateEngine');
+const createMockOutput = require('../../__tests__/createMock');
+const prepareI18n = require('../prepareI18n');
+const createTemplateEngine = require('../createTemplateEngine');
 
-var WebsiteGenerator = require('../');
+const WebsiteGenerator = require('../');
 
 describe('i18n', function() {
     it('should correctly use english as default language', function() {
@@ -13,8 +13,8 @@ describe('i18n', function() {
             return prepareI18n(output);
         })
         .then(function(output) {
-            var engine = createTemplateEngine(output, 'README.md');
-            var t = engine.getFilters().get('t');
+            const engine = createTemplateEngine(output, 'README.md');
+            const t = engine.getFilters().get('t');
 
             expect(t('SUMMARY_INTRODUCTION')).toEqual('Introduction');
         });
@@ -29,8 +29,8 @@ describe('i18n', function() {
             return prepareI18n(output);
         })
         .then(function(output) {
-            var engine = createTemplateEngine(output, 'README.md');
-            var t = engine.getFilters().get('t');
+            const engine = createTemplateEngine(output, 'README.md');
+            const t = engine.getFilters().get('t');
 
             expect(t('GITBOOK_LINK')).toEqual('Publié avec GitBook');
         });
diff --git a/packages/gitbook/lib/output/website/copyPluginAssets.js b/packages/gitbook/src/output/website/copyPluginAssets.js
index 9150636..315804a 100644
--- a/packages/gitbook/lib/output/website/copyPluginAssets.js
+++ b/packages/gitbook/src/output/website/copyPluginAssets.js
@@ -1,8 +1,8 @@
-var path = require('path');
+const path = require('path');
 
-var ASSET_FOLDER = require('../../constants/pluginAssetsFolder');
-var Promise = require('../../utils/promise');
-var fs = require('../../utils/fs');
+const ASSET_FOLDER = require('../../constants/pluginAssetsFolder');
+const Promise = require('../../utils/promise');
+const fs = require('../../utils/fs');
 
 /**
     Copy all assets from plugins.
@@ -13,7 +13,7 @@ var fs = require('../../utils/fs');
     @return {Promise}
 */
 function copyPluginAssets(output) {
-    var book = output.getBook();
+    const book = output.getBook();
 
     // Don't copy plugins assets for language book
     // It'll be resolved to the parent folder
@@ -21,7 +21,7 @@ function copyPluginAssets(output) {
         return Promise(output);
     }
 
-    var plugins = output.getPlugins()
+    const plugins = output.getPlugins()
 
         // We reverse the order of plugins to copy
         // so that first plugins can replace assets from other plugins.
@@ -43,15 +43,15 @@ function copyPluginAssets(output) {
     @return {Promise}
 */
 function copyAssets(output, plugin) {
-    var logger = output.getLogger();
-    var pluginRoot = plugin.getPath();
-    var options = output.getOptions();
+    const logger = output.getLogger();
+    const pluginRoot = plugin.getPath();
+    const options = output.getOptions();
 
-    var outputRoot = options.get('root');
-    var assetOutputFolder = path.join(outputRoot, 'gitbook');
-    var prefix = options.get('prefix');
+    const outputRoot = options.get('root');
+    const assetOutputFolder = path.join(outputRoot, 'gitbook');
+    const prefix = options.get('prefix');
 
-    var assetFolder = path.join(pluginRoot, ASSET_FOLDER, prefix);
+    const assetFolder = path.join(pluginRoot, ASSET_FOLDER, prefix);
 
     if (!fs.existsSync(assetFolder)) {
         return Promise();
@@ -76,19 +76,19 @@ function copyAssets(output, plugin) {
     @return {Promise}
 */
 function copyResources(output, plugin) {
-    var logger = output.getLogger();
+    const logger = output.getLogger();
 
-    var options    = output.getOptions();
-    var outputRoot = options.get('root');
+    const options    = output.getOptions();
+    const outputRoot = options.get('root');
 
-    var state = output.getState();
-    var resources = state.getResources();
+    const state = output.getState();
+    const resources = state.getResources();
 
-    var pluginRoot      = plugin.getPath();
-    var pluginResources = resources.get(plugin.getName());
+    const pluginRoot      = plugin.getPath();
+    const pluginResources = resources.get(plugin.getName());
 
-    var assetsFolder = pluginResources.get('assets');
-    var assetOutputFolder = path.join(outputRoot, 'gitbook', plugin.getNpmID());
+    let assetsFolder = pluginResources.get('assets');
+    const assetOutputFolder = path.join(outputRoot, 'gitbook', plugin.getNpmID());
 
     if (!assetsFolder) {
         return Promise();
diff --git a/packages/gitbook/lib/output/website/createTemplateEngine.js b/packages/gitbook/src/output/website/createTemplateEngine.js
index 02ec796..42a0bea 100644
--- a/packages/gitbook/lib/output/website/createTemplateEngine.js
+++ b/packages/gitbook/src/output/website/createTemplateEngine.js
@@ -1,21 +1,21 @@
-var path = require('path');
-var nunjucks = require('nunjucks');
-var DoExtension = require('nunjucks-do')(nunjucks);
-
-var Api = require('../../api');
-var deprecate = require('../../api/deprecate');
-var JSONUtils = require('../../json');
-var LocationUtils = require('../../utils/location');
-var fs = require('../../utils/fs');
-var PathUtils = require('../../utils/path');
-var TemplateEngine = require('../../models/templateEngine');
-var templatesFolder = require('../../constants/templatesFolder');
-var defaultFilters = require('../../constants/defaultFilters');
-var Templating = require('../../templating');
-var listSearchPaths = require('./listSearchPaths');
-
-var fileToURL = require('../helper/fileToURL');
-var resolveFileToURL = require('../helper/resolveFileToURL');
+const path = require('path');
+const nunjucks = require('nunjucks');
+const DoExtension = require('nunjucks-do')(nunjucks);
+
+const Api = require('../../api');
+const deprecate = require('../../api/deprecate');
+const JSONUtils = require('../../json');
+const LocationUtils = require('../../utils/location');
+const fs = require('../../utils/fs');
+const PathUtils = require('../../utils/path');
+const TemplateEngine = require('../../models/templateEngine');
+const templatesFolder = require('../../constants/templatesFolder');
+const defaultFilters = require('../../constants/defaultFilters');
+const Templating = require('../../templating');
+const listSearchPaths = require('./listSearchPaths');
+
+const fileToURL = require('../helper/fileToURL');
+const resolveFileToURL = require('../helper/resolveFileToURL');
 
 /**
  * Directory for a theme with the templates
@@ -32,25 +32,25 @@ function templateFolder(dir) {
  * @return {TemplateEngine}
  */
 function createTemplateEngine(output, currentFile) {
-    var book = output.getBook();
-    var state = output.getState();
-    var i18n = state.getI18n();
-    var config = book.getConfig();
-    var summary = book.getSummary();
-    var outputFolder = output.getRoot();
+    const book = output.getBook();
+    const state = output.getState();
+    const i18n = state.getI18n();
+    const config = book.getConfig();
+    const summary = book.getSummary();
+    const outputFolder = output.getRoot();
 
     // Search paths for templates
-    var searchPaths = listSearchPaths(output);
-    var tplSearchPaths = searchPaths.map(templateFolder);
+    const searchPaths = listSearchPaths(output);
+    const tplSearchPaths = searchPaths.map(templateFolder);
 
     // Create loader
-    var loader = new Templating.ThemesLoader(tplSearchPaths);
+    const loader = new Templating.ThemesLoader(tplSearchPaths);
 
     // Get languages
-    var language = config.getValue('language');
+    const language = config.getValue('language');
 
     // Create API context
-    var context = Api.encodeGlobal(output);
+    const context = Api.encodeGlobal(output);
 
 
     /**
@@ -63,7 +63,7 @@ function createTemplateEngine(output, currentFile) {
             return false;
         }
 
-        var filePath = PathUtils.resolveInRoot(outputFolder, fileName);
+        const filePath = PathUtils.resolveInRoot(outputFolder, fileName);
         return fs.existsSync(filePath);
     }
 
@@ -73,7 +73,7 @@ function createTemplateEngine(output, currentFile) {
      * @return {Object|undefined}
      */
     function getArticleByPath(filePath) {
-        var article = summary.getByPath(filePath);
+        const article = summary.getByPath(filePath);
         if (!article) return undefined;
 
         return JSONUtils.encodeSummaryArticle(article);
@@ -85,24 +85,25 @@ function createTemplateEngine(output, currentFile) {
      * @return {Object|undefined}
      */
     function getPageByPath(filePath) {
-        var page = output.getPage(filePath);
+        const page = output.getPage(filePath);
         if (!page) return undefined;
 
         return JSONUtils.encodePage(page, summary);
     }
 
     return TemplateEngine.create({
-        loader: loader,
+        loader,
 
-        context: context,
+        context,
 
         globals: {
-            getArticleByPath: getArticleByPath,
-            getPageByPath: getPageByPath,
-            fileExists: fileExists
+            getArticleByPath,
+            getPageByPath,
+            fileExists
         },
 
         filters: defaultFilters.merge({
+
             /**
              * Translate a sentence
              */
@@ -115,12 +116,12 @@ function createTemplateEngine(output, currentFile) {
              * relative path.
              * it also resolve pages
              */
-            resolveFile: function(filePath) {
+            resolveFile(filePath) {
                 filePath = resolveFileToURL(output, filePath);
                 return LocationUtils.relativeForFile(currentFile, filePath);
             },
 
-            resolveAsset: function(filePath) {
+            resolveAsset(filePath) {
                 filePath = LocationUtils.toAbsolute(filePath, '', '');
                 filePath = path.join('gitbook', filePath);
                 filePath = LocationUtils.relativeForFile(currentFile, filePath);
@@ -137,7 +138,7 @@ function createTemplateEngine(output, currentFile) {
             fileExists: deprecate.method(book, 'fileExists', fileExists, 'Filter "fileExists" is deprecated, use "fileExists(filename)" '),
             getArticleByPath: deprecate.method(book, 'getArticleByPath', fileExists, 'Filter "getArticleByPath" is deprecated, use "getArticleByPath(filename)" '),
 
-            contentURL: function(filePath) {
+            contentURL(filePath) {
                 return fileToURL(output, filePath);
             }
         }),
diff --git a/packages/gitbook/lib/output/website/index.js b/packages/gitbook/src/output/website/index.js
index 7818a28..7818a28 100644
--- a/packages/gitbook/lib/output/website/index.js
+++ b/packages/gitbook/src/output/website/index.js
diff --git a/packages/gitbook/lib/output/website/listSearchPaths.js b/packages/gitbook/src/output/website/listSearchPaths.js
index c45f39c..c07dade 100644
--- a/packages/gitbook/lib/output/website/listSearchPaths.js
+++ b/packages/gitbook/src/output/website/listSearchPaths.js
@@ -6,10 +6,10 @@
     @return {List<String>}
 */
 function listSearchPaths(output) {
-    var book = output.getBook();
-    var plugins = output.getPlugins();
+    const book = output.getBook();
+    const plugins = output.getPlugins();
 
-    var searchPaths = plugins
+    const searchPaths = plugins
         .valueSeq()
         .map(function(plugin) {
             return plugin.getPath();
diff --git a/packages/gitbook/lib/output/website/onAsset.js b/packages/gitbook/src/output/website/onAsset.js
index 69dfc4f..b996375 100644
--- a/packages/gitbook/lib/output/website/onAsset.js
+++ b/packages/gitbook/src/output/website/onAsset.js
@@ -1,5 +1,5 @@
-var path = require('path');
-var fs = require('../../utils/fs');
+const path = require('path');
+const fs = require('../../utils/fs');
 
 /**
     Copy an asset to the output folder
@@ -8,12 +8,12 @@ var fs = require('../../utils/fs');
     @param {Page} page
 */
 function onAsset(output, asset) {
-    var book = output.getBook();
-    var options = output.getOptions();
-    var bookFS = book.getContentFS();
+    const book = output.getBook();
+    const options = output.getOptions();
+    const bookFS = book.getContentFS();
 
-    var outputFolder = options.get('root');
-    var outputPath = path.resolve(outputFolder, asset);
+    const outputFolder = options.get('root');
+    const outputPath = path.resolve(outputFolder, asset);
 
     return fs.ensureFile(outputPath)
     .then(function() {
diff --git a/packages/gitbook/src/output/website/onFinish.js b/packages/gitbook/src/output/website/onFinish.js
new file mode 100644
index 0000000..b032c90
--- /dev/null
+++ b/packages/gitbook/src/output/website/onFinish.js
@@ -0,0 +1,35 @@
+const Promise = require('../../utils/promise');
+const JSONUtils = require('../../json');
+const Templating = require('../../templating');
+const writeFile = require('../helper/writeFile');
+const createTemplateEngine = require('./createTemplateEngine');
+
+/**
+    Finish the generation, write the languages index
+
+    @param {Output}
+    @return {Output}
+*/
+function onFinish(output) {
+    const book = output.getBook();
+    const options = output.getOptions();
+    const prefix = options.get('prefix');
+
+    if (!book.isMultilingual()) {
+        return Promise(output);
+    }
+
+    const filePath = 'index.html';
+    const engine = createTemplateEngine(output, filePath);
+    const context = JSONUtils.encodeOutput(output);
+
+    // Render the theme
+    return Templating.renderFile(engine, prefix + '/languages.html', context)
+
+    // Write it to the disk
+    .then(function(tplOut) {
+        return writeFile(output, filePath, tplOut.getContent());
+    });
+}
+
+module.exports = onFinish;
diff --git a/packages/gitbook/lib/output/website/onInit.js b/packages/gitbook/src/output/website/onInit.js
index 3465eef..3f6d26e 100644
--- a/packages/gitbook/lib/output/website/onInit.js
+++ b/packages/gitbook/src/output/website/onInit.js
@@ -1,8 +1,8 @@
-var Promise = require('../../utils/promise');
+const Promise = require('../../utils/promise');
 
-var copyPluginAssets = require('./copyPluginAssets');
-var prepareI18n = require('./prepareI18n');
-var prepareResources = require('./prepareResources');
+const copyPluginAssets = require('./copyPluginAssets');
+const prepareI18n = require('./prepareI18n');
+const prepareResources = require('./prepareResources');
 
 /**
     Initialize the generator
diff --git a/packages/gitbook/lib/output/website/onPage.js b/packages/gitbook/src/output/website/onPage.js
index 5fb40a7..3b40536 100644
--- a/packages/gitbook/lib/output/website/onPage.js
+++ b/packages/gitbook/src/output/website/onPage.js
@@ -1,15 +1,15 @@
-var path = require('path');
-var omit = require('omit-keys');
+const path = require('path');
+const omit = require('omit-keys');
 
-var Templating = require('../../templating');
-var Plugins = require('../../plugins');
-var JSONUtils = require('../../json');
-var LocationUtils = require('../../utils/location');
-var Modifiers = require('../modifiers');
-var writeFile = require('../helper/writeFile');
-var getModifiers = require('../getModifiers');
-var createTemplateEngine = require('./createTemplateEngine');
-var fileToOutput = require('../helper/fileToOutput');
+const Templating = require('../../templating');
+const Plugins = require('../../plugins');
+const JSONUtils = require('../../json');
+const LocationUtils = require('../../utils/location');
+const Modifiers = require('../modifiers');
+const writeFile = require('../helper/writeFile');
+const getModifiers = require('../getModifiers');
+const createTemplateEngine = require('./createTemplateEngine');
+const fileToOutput = require('../helper/fileToOutput');
 
 /**
  * Write a page as a json file
@@ -18,41 +18,41 @@ var fileToOutput = require('../helper/fileToOutput');
  * @param {Page} page
  */
 function onPage(output, page) {
-    var options   = output.getOptions();
-    var prefix    = options.get('prefix');
+    const options   = output.getOptions();
+    const prefix    = options.get('prefix');
 
-    var file      = page.getFile();
+    const file      = page.getFile();
 
-    var book      = output.getBook();
-    var plugins   = output.getPlugins();
-    var state     = output.getState();
-    var resources = state.getResources();
+    const book      = output.getBook();
+    const plugins   = output.getPlugins();
+    const state     = output.getState();
+    const resources = state.getResources();
 
-    var engine = createTemplateEngine(output, page.getPath());
+    const engine = createTemplateEngine(output, page.getPath());
 
     // Output file path
-    var filePath = fileToOutput(output, file.getPath());
+    const filePath = fileToOutput(output, file.getPath());
 
     // Calcul relative path to the root
-    var outputDirName = path.dirname(filePath);
-    var basePath = LocationUtils.normalize(path.relative(outputDirName, './'));
+    const outputDirName = path.dirname(filePath);
+    const basePath = LocationUtils.normalize(path.relative(outputDirName, './'));
 
     return Modifiers.modifyHTML(page, getModifiers(output, page))
     .then(function(resultPage) {
         // Generate the context
-        var context = JSONUtils.encodeOutputWithPage(output, resultPage);
+        const context = JSONUtils.encodeOutputWithPage(output, resultPage);
         context.plugins = {
             resources: Plugins.listResources(plugins, resources).toJS()
         };
 
         context.template = {
-            getJSContext: function() {
+            getJSContext() {
                 return {
                     page: omit(context.page, 'content'),
                     config: context.config,
                     file: context.file,
                     gitbook: context.gitbook,
-                    basePath: basePath,
+                    basePath,
                     book: {
                         language: book.getLanguage()
                     }
diff --git a/packages/gitbook/lib/output/website/options.js b/packages/gitbook/src/output/website/options.js
index ac9cdad..43314df 100644
--- a/packages/gitbook/lib/output/website/options.js
+++ b/packages/gitbook/src/output/website/options.js
@@ -1,6 +1,6 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var Options = Immutable.Record({
+const Options = Immutable.Record({
     // Root folder for the output
     root:               String(),
 
diff --git a/packages/gitbook/lib/output/website/prepareI18n.js b/packages/gitbook/src/output/website/prepareI18n.js
index cedd3b9..b02ef77 100644
--- a/packages/gitbook/lib/output/website/prepareI18n.js
+++ b/packages/gitbook/src/output/website/prepareI18n.js
@@ -1,8 +1,8 @@
-var path = require('path');
+const path = require('path');
 
-var fs = require('../../utils/fs');
-var Promise = require('../../utils/promise');
-var listSearchPaths = require('./listSearchPaths');
+const fs = require('../../utils/fs');
+const Promise = require('../../utils/promise');
+const listSearchPaths = require('./listSearchPaths');
 
 /**
  * Prepare i18n, load translations from plugins and book
@@ -11,14 +11,14 @@ var listSearchPaths = require('./listSearchPaths');
  * @return {Promise<Output>}
  */
 function prepareI18n(output) {
-    var state = output.getState();
-    var i18n = state.getI18n();
-    var searchPaths = listSearchPaths(output);
+    const state = output.getState();
+    const i18n = state.getI18n();
+    const searchPaths = listSearchPaths(output);
 
     searchPaths
         .reverse()
         .forEach(function(searchPath) {
-            var i18nRoot = path.resolve(searchPath, '_i18n');
+            const i18nRoot = path.resolve(searchPath, '_i18n');
 
             if (!fs.existsSync(i18nRoot)) return;
             i18n.load(i18nRoot);
diff --git a/packages/gitbook/lib/output/website/prepareResources.js b/packages/gitbook/src/output/website/prepareResources.js
index 4e6835d..e93f45f 100644
--- a/packages/gitbook/lib/output/website/prepareResources.js
+++ b/packages/gitbook/src/output/website/prepareResources.js
@@ -1,8 +1,8 @@
-var is        = require('is');
-var Immutable = require('immutable');
-var Promise   = require('../../utils/promise');
+const is        = require('is');
+const Immutable = require('immutable');
+const Promise   = require('../../utils/promise');
 
-var Api              = require('../../api');
+const Api              = require('../../api');
 
 /**
     Prepare plugins resources, add all output corresponding type resources
@@ -11,16 +11,16 @@ var Api              = require('../../api');
     @return {Promise<Output>}
 */
 function prepareResources(output) {
-    var plugins = output.getPlugins();
-    var options = output.getOptions();
-    var type    = options.get('prefix');
-    var state   = output.getState();
-    var context = Api.encodeGlobal(output);
+    const plugins = output.getPlugins();
+    const options = output.getOptions();
+    const type    = options.get('prefix');
+    let state   = output.getState();
+    const context = Api.encodeGlobal(output);
 
-    var result = Immutable.Map();
+    let result = Immutable.Map();
 
     return Promise.forEach(plugins, function(plugin) {
-        var pluginResources = plugin.getResources(type);
+        const pluginResources = plugin.getResources(type);
 
         return Promise()
         .then(function() {
@@ -44,11 +44,11 @@ function prepareResources(output) {
         });
 
         output = output.merge({
-            state: state
+            state
         });
 
         return output;
     });
 }
 
-module.exports = prepareResources;
\ No newline at end of file
+module.exports = prepareResources;
diff --git a/packages/gitbook/lib/output/website/state.js b/packages/gitbook/src/output/website/state.js
index cb8f750..813b850 100644
--- a/packages/gitbook/lib/output/website/state.js
+++ b/packages/gitbook/src/output/website/state.js
@@ -1,7 +1,7 @@
-var I18n = require('i18n-t');
-var Immutable = require('immutable');
+const I18n = require('i18n-t');
+const Immutable = require('immutable');
 
-var GeneratorState = Immutable.Record({
+const GeneratorState = Immutable.Record({
     i18n:       I18n(),
 
     // List of plugins' resources
diff --git a/packages/gitbook/lib/parse/__tests__/listAssets.js b/packages/gitbook/src/parse/__tests__/listAssets.js
index 4c5b0a0..102aed9 100644
--- a/packages/gitbook/lib/parse/__tests__/listAssets.js
+++ b/packages/gitbook/src/parse/__tests__/listAssets.js
@@ -1,20 +1,20 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var Book = require('../../models/book');
-var createMockFS = require('../../fs/mock');
-var listAssets = require('../listAssets');
-var parseGlossary = require('../parseGlossary');
+const Book = require('../../models/book');
+const createMockFS = require('../../fs/mock');
+const listAssets = require('../listAssets');
+const parseGlossary = require('../parseGlossary');
 
 describe('listAssets', function() {
     it('should not list glossary as asset', function() {
-        var fs = createMockFS({
+        const fs = createMockFS({
             'GLOSSARY.md': '# Glossary\n\n## Hello\nDescription for hello',
             'assetFile.js': '',
             'assets': {
                 'file.js': ''
             }
         });
-        var book = Book.createForFS(fs);
+        const book = Book.createForFS(fs);
 
         return parseGlossary(book)
         .then(function(resultBook) {
diff --git a/packages/gitbook/lib/parse/__tests__/parseBook.js b/packages/gitbook/src/parse/__tests__/parseBook.js
index b1236c9..d5de25c 100644
--- a/packages/gitbook/lib/parse/__tests__/parseBook.js
+++ b/packages/gitbook/src/parse/__tests__/parseBook.js
@@ -1,11 +1,11 @@
-var Book = require('../../models/book');
-var createMockFS = require('../../fs/mock');
+const Book = require('../../models/book');
+const createMockFS = require('../../fs/mock');
 
 describe('parseBook', function() {
-    var parseBook = require('../parseBook');
+    const parseBook = require('../parseBook');
 
     it('should parse multilingual book', function() {
-        var fs = createMockFS({
+        const fs = createMockFS({
             'LANGS.md': '# Languages\n\n* [en](en)\n* [fr](fr)',
             'en': {
                 'README.md': 'Hello'
@@ -14,12 +14,12 @@ describe('parseBook', function() {
                 'README.md': 'Bonjour'
             }
         });
-        var book = Book.createForFS(fs);
+        const book = Book.createForFS(fs);
 
         return parseBook(book)
         .then(function(resultBook) {
-            var languages = resultBook.getLanguages();
-            var books = resultBook.getBooks();
+            const languages = resultBook.getLanguages();
+            const books = resultBook.getBooks();
 
             expect(resultBook.isMultilingual()).toBe(true);
             expect(languages.getList().size).toBe(2);
@@ -28,7 +28,7 @@ describe('parseBook', function() {
     });
 
     it('should extend configuration for multilingual book', function() {
-        var fs = createMockFS({
+        const fs = createMockFS({
             'LANGS.md': '# Languages\n\n* [en](en)\n* [fr](fr)',
             'book.json': '{ "title": "Test", "author": "GitBook" }',
             'en': {
@@ -39,20 +39,20 @@ describe('parseBook', function() {
                 'README.md': 'Bonjour'
             }
         });
-        var book = Book.createForFS(fs);
+        const book = Book.createForFS(fs);
 
         return parseBook(book)
         .then(function(resultBook) {
-            var books = resultBook.getBooks();
+            const books = resultBook.getBooks();
 
             expect(resultBook.isMultilingual()).toBe(true);
             expect(books.size).toBe(2);
 
-            var en = books.get('en');
-            var fr = books.get('fr');
+            const en = books.get('en');
+            const fr = books.get('fr');
 
-            var enConfig = en.getConfig();
-            var frConfig = fr.getConfig();
+            const enConfig = en.getConfig();
+            const frConfig = fr.getConfig();
 
             expect(enConfig.getValue('title')).toBe('Test EN');
             expect(enConfig.getValue('author')).toBe('GitBook');
@@ -63,7 +63,7 @@ describe('parseBook', function() {
     });
 
     it('should parse book in a directory', function() {
-        var fs = createMockFS({
+        const fs = createMockFS({
             'book.json': JSON.stringify({
                 root: './test'
             }),
@@ -73,13 +73,13 @@ describe('parseBook', function() {
                 'page.md': 'Page'
             }
         });
-        var book = Book.createForFS(fs);
+        const book = Book.createForFS(fs);
 
         return parseBook(book)
         .then(function(resultBook) {
-            var readme = resultBook.getReadme();
-            var summary = resultBook.getSummary();
-            var articles = summary.getArticlesAsList();
+            const readme = resultBook.getReadme();
+            const summary = resultBook.getSummary();
+            const articles = summary.getArticlesAsList();
 
             expect(summary.getFile().exists()).toBe(true);
             expect(readme.getFile().exists()).toBe(true);
diff --git a/packages/gitbook/lib/parse/__tests__/parseGlossary.js b/packages/gitbook/src/parse/__tests__/parseGlossary.js
index 9069af6..ba2e407 100644
--- a/packages/gitbook/lib/parse/__tests__/parseGlossary.js
+++ b/packages/gitbook/src/parse/__tests__/parseGlossary.js
@@ -1,20 +1,20 @@
-var Book = require('../../models/book');
-var createMockFS = require('../../fs/mock');
+const Book = require('../../models/book');
+const createMockFS = require('../../fs/mock');
 
 describe('parseGlossary', function() {
-    var parseGlossary = require('../parseGlossary');
+    const parseGlossary = require('../parseGlossary');
 
     it('should parse glossary if exists', function() {
-        var fs = createMockFS({
+        const fs = createMockFS({
             'GLOSSARY.md': '# Glossary\n\n## Hello\nDescription for hello'
         });
-        var book = Book.createForFS(fs);
+        const book = Book.createForFS(fs);
 
         return parseGlossary(book)
         .then(function(resultBook) {
-            var glossary = resultBook.getGlossary();
-            var file = glossary.getFile();
-            var entries = glossary.getEntries();
+            const glossary = resultBook.getGlossary();
+            const file = glossary.getFile();
+            const entries = glossary.getEntries();
 
             expect(file.exists()).toBeTruthy();
             expect(entries.size).toBe(1);
@@ -22,13 +22,13 @@ describe('parseGlossary', function() {
     });
 
     it('should not fail if doesn\'t exist', function() {
-        var fs = createMockFS({});
-        var book = Book.createForFS(fs);
+        const fs = createMockFS({});
+        const book = Book.createForFS(fs);
 
         return parseGlossary(book)
         .then(function(resultBook) {
-            var glossary = resultBook.getGlossary();
-            var file = glossary.getFile();
+            const glossary = resultBook.getGlossary();
+            const file = glossary.getFile();
 
             expect(file.exists()).toBeFalsy();
         });
diff --git a/packages/gitbook/lib/parse/__tests__/parseIgnore.js b/packages/gitbook/src/parse/__tests__/parseIgnore.js
index 54e7dae..b1bd43c 100644
--- a/packages/gitbook/lib/parse/__tests__/parseIgnore.js
+++ b/packages/gitbook/src/parse/__tests__/parseIgnore.js
@@ -1,9 +1,9 @@
-var Book = require('../../models/book');
-var createMockFS = require('../../fs/mock');
+const Book = require('../../models/book');
+const createMockFS = require('../../fs/mock');
 
 describe('parseIgnore', function() {
-    var parseIgnore = require('../parseIgnore');
-    var fs = createMockFS({
+    const parseIgnore = require('../parseIgnore');
+    const fs = createMockFS({
         '.ignore': 'test-1.js',
         '.gitignore': 'test-2.js\ntest-3.js',
         '.bookignore': '!test-3.js',
@@ -13,7 +13,7 @@ describe('parseIgnore', function() {
     });
 
     function getBook() {
-        var book = Book.createForFS(fs);
+        const book = Book.createForFS(fs);
         return parseIgnore(book);
     }
 
diff --git a/packages/gitbook/lib/parse/__tests__/parsePageFromString.js b/packages/gitbook/src/parse/__tests__/parsePageFromString.js
index 2911fa3..13bc544 100644
--- a/packages/gitbook/lib/parse/__tests__/parsePageFromString.js
+++ b/packages/gitbook/src/parse/__tests__/parsePageFromString.js
@@ -1,25 +1,25 @@
-var parsePageFromString = require('../parsePageFromString');
-var Page = require('../../models/page');
+const parsePageFromString = require('../parsePageFromString');
+const Page = require('../../models/page');
 
 describe('parsePageFromString', function() {
-    var page = new Page();
+    const page = new Page();
 
     it('should parse YAML frontmatter', function() {
-        var CONTENT = '---\nhello: true\nworld: "cool"\n---\n# Hello World\n';
-        var newPage = parsePageFromString(page, CONTENT);
+        const CONTENT = '---\nhello: true\nworld: "cool"\n---\n# Hello World\n';
+        const newPage = parsePageFromString(page, CONTENT);
 
         expect(newPage.getDir()).toBe('ltr');
         expect(newPage.getContent()).toBe('# Hello World\n');
 
-        var attrs = newPage.getAttributes();
+        const attrs = newPage.getAttributes();
         expect(attrs.size).toBe(2);
         expect(attrs.get('hello')).toBe(true);
         expect(attrs.get('world')).toBe('cool');
     });
 
     it('should parse text direction (english)', function() {
-        var CONTENT = 'Hello World';
-        var newPage = parsePageFromString(page, CONTENT);
+        const CONTENT = 'Hello World';
+        const newPage = parsePageFromString(page, CONTENT);
 
         expect(newPage.getDir()).toBe('ltr');
         expect(newPage.getContent()).toBe('Hello World');
@@ -27,8 +27,8 @@ describe('parsePageFromString', function() {
     });
 
     it('should parse text direction (arab)', function() {
-        var CONTENT = 'مرحبا بالعالم';
-        var newPage = parsePageFromString(page, CONTENT);
+        const CONTENT = 'مرحبا بالعالم';
+        const newPage = parsePageFromString(page, CONTENT);
 
         expect(newPage.getDir()).toBe('rtl');
         expect(newPage.getContent()).toBe('مرحبا بالعالم');
diff --git a/packages/gitbook/lib/parse/__tests__/parseReadme.js b/packages/gitbook/src/parse/__tests__/parseReadme.js
index 4270ea3..45ecfa3 100644
--- a/packages/gitbook/lib/parse/__tests__/parseReadme.js
+++ b/packages/gitbook/src/parse/__tests__/parseReadme.js
@@ -1,20 +1,20 @@
-var Promise = require('../../utils/promise');
-var Book = require('../../models/book');
-var createMockFS = require('../../fs/mock');
+const Promise = require('../../utils/promise');
+const Book = require('../../models/book');
+const createMockFS = require('../../fs/mock');
 
 describe('parseReadme', function() {
-    var parseReadme = require('../parseReadme');
+    const parseReadme = require('../parseReadme');
 
     it('should parse summary if exists', function() {
-        var fs = createMockFS({
+        const fs = createMockFS({
             'README.md': '# Hello\n\nAnd here is the description.'
         });
-        var book = Book.createForFS(fs);
+        const book = Book.createForFS(fs);
 
         return parseReadme(book)
         .then(function(resultBook) {
-            var readme = resultBook.getReadme();
-            var file = readme.getFile();
+            const readme = resultBook.getReadme();
+            const file = readme.getFile();
 
             expect(file.exists()).toBeTruthy();
             expect(readme.getTitle()).toBe('Hello');
@@ -23,8 +23,8 @@ describe('parseReadme', function() {
     });
 
     it('should fail if doesn\'t exist', function() {
-        var fs = createMockFS({});
-        var book = Book.createForFS(fs);
+        const fs = createMockFS({});
+        const book = Book.createForFS(fs);
 
         return parseReadme(book)
         .then(function(resultBook) {
diff --git a/packages/gitbook/lib/parse/__tests__/parseSummary.js b/packages/gitbook/src/parse/__tests__/parseSummary.js
index 55a445e..8b86c45 100644
--- a/packages/gitbook/lib/parse/__tests__/parseSummary.js
+++ b/packages/gitbook/src/parse/__tests__/parseSummary.js
@@ -1,32 +1,32 @@
-var Book = require('../../models/book');
-var createMockFS = require('../../fs/mock');
+const Book = require('../../models/book');
+const createMockFS = require('../../fs/mock');
 
 describe('parseSummary', function() {
-    var parseSummary = require('../parseSummary');
+    const parseSummary = require('../parseSummary');
 
     it('should parse summary if exists', function() {
-        var fs = createMockFS({
+        const fs = createMockFS({
             'SUMMARY.md': '# Summary\n\n* [Hello](hello.md)'
         });
-        var book = Book.createForFS(fs);
+        const book = Book.createForFS(fs);
 
         return parseSummary(book)
         .then(function(resultBook) {
-            var summary = resultBook.getSummary();
-            var file = summary.getFile();
+            const summary = resultBook.getSummary();
+            const file = summary.getFile();
 
             expect(file.exists()).toBeTruthy();
         });
     });
 
     it('should not fail if doesn\'t exist', function() {
-        var fs = createMockFS({});
-        var book = Book.createForFS(fs);
+        const fs = createMockFS({});
+        const book = Book.createForFS(fs);
 
         return parseSummary(book)
         .then(function(resultBook) {
-            var summary = resultBook.getSummary();
-            var file = summary.getFile();
+            const summary = resultBook.getSummary();
+            const file = summary.getFile();
 
             expect(file.exists()).toBeFalsy();
         });
diff --git a/packages/gitbook/lib/parse/findParsableFile.js b/packages/gitbook/src/parse/findParsableFile.js
index 51e2dd0..c30dbbd 100644
--- a/packages/gitbook/lib/parse/findParsableFile.js
+++ b/packages/gitbook/src/parse/findParsableFile.js
@@ -1,7 +1,7 @@
-var path = require('path');
+const path = require('path');
 
-var Promise = require('../utils/promise');
-var parsers = require('../parsers');
+const Promise = require('../utils/promise');
+const parsers = require('../parsers');
 
 /**
     Find a file parsable (Markdown or AsciiDoc) in a book
@@ -11,16 +11,16 @@ var parsers = require('../parsers');
     @return {Promise<File | Undefined>}
 */
 function findParsableFile(book, filename) {
-    var fs = book.getContentFS();
-    var ext = path.extname(filename);
-    var basename = path.basename(filename, ext);
-    var basedir = path.dirname(filename);
+    const fs = book.getContentFS();
+    const ext = path.extname(filename);
+    const basename = path.basename(filename, ext);
+    const basedir = path.dirname(filename);
 
     // Ordered list of extensions to test
-    var exts = parsers.extensions;
+    const exts = parsers.extensions;
 
     return Promise.some(exts, function(ext) {
-        var filepath = basename + ext;
+        const filepath = basename + ext;
 
         return fs.findFile(basedir, filepath)
         .then(function(found) {
diff --git a/packages/gitbook/lib/parse/index.js b/packages/gitbook/src/parse/index.js
index 1f73946..1f73946 100644
--- a/packages/gitbook/lib/parse/index.js
+++ b/packages/gitbook/src/parse/index.js
diff --git a/packages/gitbook/lib/parse/listAssets.js b/packages/gitbook/src/parse/listAssets.js
index d83d8fd..07cf2e1 100644
--- a/packages/gitbook/lib/parse/listAssets.js
+++ b/packages/gitbook/src/parse/listAssets.js
@@ -1,4 +1,4 @@
-var timing = require('../utils/timing');
+const timing = require('../utils/timing');
 
 /**
     List all assets in a book
@@ -9,19 +9,19 @@ var timing = require('../utils/timing');
     @param
 */
 function listAssets(book, pages) {
-    var fs = book.getContentFS();
+    const fs = book.getContentFS();
 
-    var summary = book.getSummary();
-    var summaryFile = summary.getFile().getPath();
+    const summary = book.getSummary();
+    const summaryFile = summary.getFile().getPath();
 
-    var glossary = book.getGlossary();
-    var glossaryFile = glossary.getFile().getPath();
+    const glossary = book.getGlossary();
+    const glossaryFile = glossary.getFile().getPath();
 
-    var langs = book.getLanguages();
-    var langsFile = langs.getFile().getPath();
+    const langs = book.getLanguages();
+    const langsFile = langs.getFile().getPath();
 
-    var config = book.getConfig();
-    var configFile = config.getFile().getPath();
+    const config = book.getConfig();
+    const configFile = config.getFile().getPath();
 
     function filterFile(file) {
         return !(
diff --git a/packages/gitbook/lib/parse/lookupStructureFile.js b/packages/gitbook/src/parse/lookupStructureFile.js
index 36b37f8..e54a769 100644
--- a/packages/gitbook/lib/parse/lookupStructureFile.js
+++ b/packages/gitbook/src/parse/lookupStructureFile.js
@@ -1,4 +1,4 @@
-var findParsableFile = require('./findParsableFile');
+const findParsableFile = require('./findParsableFile');
 
 /**
     Lookup a structure file (ex: SUMMARY.md, GLOSSARY.md) in a book. Uses
@@ -10,9 +10,9 @@ var findParsableFile = require('./findParsableFile');
     to the book content root.
 */
 function lookupStructureFile(book, type) {
-    var config = book.getConfig();
+    const config = book.getConfig();
 
-    var fileToSearch = config.getValue(['structure', type]);
+    const fileToSearch = config.getValue(['structure', type]);
 
     return findParsableFile(book, fileToSearch);
 }
diff --git a/packages/gitbook/lib/parse/parseBook.js b/packages/gitbook/src/parse/parseBook.js
index a92f39e..85f4519 100644
--- a/packages/gitbook/lib/parse/parseBook.js
+++ b/packages/gitbook/src/parse/parseBook.js
@@ -1,13 +1,13 @@
-var Promise = require('../utils/promise');
-var timing = require('../utils/timing');
-var Book = require('../models/book');
+const Promise = require('../utils/promise');
+const timing = require('../utils/timing');
+const Book = require('../models/book');
 
-var parseIgnore = require('./parseIgnore');
-var parseConfig = require('./parseConfig');
-var parseGlossary = require('./parseGlossary');
-var parseSummary = require('./parseSummary');
-var parseReadme = require('./parseReadme');
-var parseLanguages = require('./parseLanguages');
+const parseIgnore = require('./parseIgnore');
+const parseConfig = require('./parseConfig');
+const parseGlossary = require('./parseGlossary');
+const parseSummary = require('./parseSummary');
+const parseReadme = require('./parseReadme');
+const parseLanguages = require('./parseLanguages');
 
 /**
     Parse content of a book
@@ -29,13 +29,13 @@ function parseBookContent(book) {
     @return {Promise<Book>}
 */
 function parseMultilingualBook(book) {
-    var languages = book.getLanguages();
-    var langList = languages.getList();
+    const languages = book.getLanguages();
+    const langList = languages.getList();
 
     return Promise.reduce(langList, function(currentBook, lang) {
-        var langID = lang.getID();
-        var child = Book.createFromParent(currentBook, langID);
-        var ignore = currentBook.getIgnore();
+        const langID = lang.getID();
+        const child = Book.createFromParent(currentBook, langID);
+        let ignore = currentBook.getIgnore();
 
         return Promise(child)
         .then(parseConfig)
diff --git a/packages/gitbook/lib/parse/parseConfig.js b/packages/gitbook/src/parse/parseConfig.js
index a411af8..cd27426 100644
--- a/packages/gitbook/lib/parse/parseConfig.js
+++ b/packages/gitbook/src/parse/parseConfig.js
@@ -1,7 +1,7 @@
-var Promise = require('../utils/promise');
+const Promise = require('../utils/promise');
 
-var validateConfig = require('./validateConfig');
-var CONFIG_FILES = require('../constants/configFiles');
+const validateConfig = require('./validateConfig');
+const CONFIG_FILES = require('../constants/configFiles');
 
 /**
     Parse configuration from "book.json" or "book.js"
@@ -10,8 +10,8 @@ var CONFIG_FILES = require('../constants/configFiles');
     @return {Promise<Book>}
 */
 function parseConfig(book) {
-    var fs = book.getFS();
-    var config = book.getConfig();
+    const fs = book.getFS();
+    let config = book.getConfig();
 
     return Promise.some(CONFIG_FILES, function(filename) {
         // Is this file ignored?
@@ -25,19 +25,19 @@ function parseConfig(book) {
             return fs.statFile(filename)
             .then(function(file) {
                 return {
-                    file: file,
+                    file,
                     values: cfg
                 };
             });
         })
         .fail(function(err) {
-            if (err.code != 'MODULE_NOT_FOUND') throw(err);
+            if (err.code != 'MODULE_NOT_FOUND') throw (err);
             else return Promise(false);
         });
     })
 
     .then(function(result) {
-        var values = result? result.values : {};
+        let values = result ? result.values : {};
         values = validateConfig(values);
 
         // Set the file
diff --git a/packages/gitbook/lib/parse/parseGlossary.js b/packages/gitbook/src/parse/parseGlossary.js
index a96e5fc..052985b 100644
--- a/packages/gitbook/lib/parse/parseGlossary.js
+++ b/packages/gitbook/src/parse/parseGlossary.js
@@ -1,5 +1,5 @@
-var parseStructureFile = require('./parseStructureFile');
-var Glossary = require('../models/glossary');
+const parseStructureFile = require('./parseStructureFile');
+const Glossary = require('../models/glossary');
 
 /**
     Parse glossary
@@ -8,7 +8,7 @@ var Glossary = require('../models/glossary');
     @return {Promise<Book>}
 */
 function parseGlossary(book) {
-    var logger = book.getLogger();
+    const logger = book.getLogger();
 
     return parseStructureFile(book, 'glossary')
     .spread(function(file, entries) {
@@ -18,7 +18,7 @@ function parseGlossary(book) {
 
         logger.debug.ln('glossary index file found at', file.getPath());
 
-        var glossary = Glossary.createFromEntries(file, entries);
+        const glossary = Glossary.createFromEntries(file, entries);
         return book.set('glossary', glossary);
     });
 }
diff --git a/packages/gitbook/lib/parse/parseIgnore.js b/packages/gitbook/src/parse/parseIgnore.js
index 84d8c33..3059447 100644
--- a/packages/gitbook/lib/parse/parseIgnore.js
+++ b/packages/gitbook/src/parse/parseIgnore.js
@@ -1,7 +1,7 @@
-var Promise = require('../utils/promise');
-var IGNORE_FILES = require('../constants/ignoreFiles');
+const Promise = require('../utils/promise');
+const IGNORE_FILES = require('../constants/ignoreFiles');
 
-var DEFAULT_IGNORES = [
+const DEFAULT_IGNORES = [
     // Skip Git stuff
     '.git/',
 
@@ -29,8 +29,8 @@ function parseIgnore(book) {
         return Promise.reject(new Error('Ignore files could be parsed for language books'));
     }
 
-    var fs = book.getFS();
-    var ignore = book.getIgnore();
+    const fs = book.getFS();
+    let ignore = book.getIgnore();
 
     ignore = ignore.add(DEFAULT_IGNORES);
 
diff --git a/packages/gitbook/lib/parse/parseLanguages.js b/packages/gitbook/src/parse/parseLanguages.js
index 346f3a3..1b28930 100644
--- a/packages/gitbook/lib/parse/parseLanguages.js
+++ b/packages/gitbook/src/parse/parseLanguages.js
@@ -1,5 +1,5 @@
-var parseStructureFile = require('./parseStructureFile');
-var Languages = require('../models/languages');
+const parseStructureFile = require('./parseStructureFile');
+const Languages = require('../models/languages');
 
 /**
     Parse languages list from book
@@ -8,7 +8,7 @@ var Languages = require('../models/languages');
     @return {Promise<Book>}
 */
 function parseLanguages(book) {
-    var logger = book.getLogger();
+    const logger = book.getLogger();
 
     return parseStructureFile(book, 'langs')
     .spread(function(file, result) {
@@ -16,7 +16,7 @@ function parseLanguages(book) {
             return book;
         }
 
-        var languages = Languages.createFromList(file, result);
+        const languages = Languages.createFromList(file, result);
 
         logger.debug.ln('languages index file found at', file.getPath());
         logger.info.ln('parsing multilingual book, with', languages.getList().size, 'languages');
diff --git a/packages/gitbook/lib/parse/parsePage.js b/packages/gitbook/src/parse/parsePage.js
index fdc56a3..72f9ddf 100644
--- a/packages/gitbook/lib/parse/parsePage.js
+++ b/packages/gitbook/src/parse/parsePage.js
@@ -1,4 +1,4 @@
-var parsePageFromString = require('./parsePageFromString');
+const parsePageFromString = require('./parsePageFromString');
 
 /**
  * Parse a page, read its content and parse the YAMl header
@@ -8,8 +8,8 @@ var parsePageFromString = require('./parsePageFromString');
  * @return {Promise<Page>}
  */
 function parsePage(book, page) {
-    var fs = book.getContentFS();
-    var file = page.getFile();
+    const fs = book.getContentFS();
+    const file = page.getFile();
 
     return fs.readAsString(file.getPath())
     .then(function(content) {
diff --git a/packages/gitbook/lib/parse/parsePageFromString.js b/packages/gitbook/src/parse/parsePageFromString.js
index 80c147b..2e4a598 100644
--- a/packages/gitbook/lib/parse/parsePageFromString.js
+++ b/packages/gitbook/src/parse/parsePageFromString.js
@@ -1,6 +1,6 @@
-var Immutable = require('immutable');
-var fm = require('front-matter');
-var direction = require('direction');
+const Immutable = require('immutable');
+const fm = require('front-matter');
+const direction = require('direction');
 
 /**
  * Parse a page, its content and the YAMl header
@@ -9,7 +9,7 @@ var direction = require('direction');
  * @return {Page}
  */
 function parsePageFromString(page, content) {
-    var parsed = fm(content);
+    const parsed = fm(content);
 
     return page.merge({
         content:    parsed.body,
diff --git a/packages/gitbook/lib/parse/parsePagesList.js b/packages/gitbook/src/parse/parsePagesList.js
index 1cf42f5..ddac20e 100644
--- a/packages/gitbook/lib/parse/parsePagesList.js
+++ b/packages/gitbook/src/parse/parsePagesList.js
@@ -1,9 +1,9 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var timing = require('../utils/timing');
-var Page = require('../models/page');
-var walkSummary = require('./walkSummary');
-var parsePage = require('./parsePage');
+const timing = require('../utils/timing');
+const Page = require('../models/page');
+const walkSummary = require('./walkSummary');
+const parsePage = require('./parsePage');
 
 
 /**
@@ -14,11 +14,11 @@ var parsePage = require('./parsePage');
     @return {Page}
 */
 function parseFilePage(book, filePath) {
-    var fs = book.getContentFS();
+    const fs = book.getContentFS();
 
     return fs.statFile(filePath)
     .then(function(file) {
-        var page = Page.createForFile(file);
+        const page = Page.createForFile(file);
         return parsePage(book, page);
     });
 }
@@ -31,9 +31,9 @@ function parseFilePage(book, filePath) {
     @return {Promise<OrderedMap<Page>>}
 */
 function parsePagesList(book) {
-    var summary = book.getSummary();
-    var glossary = book.getGlossary();
-    var map = Immutable.OrderedMap();
+    const summary = book.getSummary();
+    const glossary = book.getGlossary();
+    let map = Immutable.OrderedMap();
 
     // Parse pages from summary
     return timing.measure(
@@ -41,7 +41,7 @@ function parsePagesList(book) {
         walkSummary(summary, function(article) {
             if (!article.isPage()) return;
 
-            var filepath = article.getPath();
+            const filepath = article.getPath();
 
             // Is the page ignored?
             if (book.isContentFileIgnored(filepath)) return;
@@ -57,7 +57,7 @@ function parsePagesList(book) {
 
     // Parse glossary
     .then(function() {
-        var file = glossary.getFile();
+        const file = glossary.getFile();
 
         if (!file.exists()) {
             return;
diff --git a/packages/gitbook/lib/parse/parseReadme.js b/packages/gitbook/src/parse/parseReadme.js
index a2ede77..82f8f19 100644
--- a/packages/gitbook/lib/parse/parseReadme.js
+++ b/packages/gitbook/src/parse/parseReadme.js
@@ -1,7 +1,7 @@
-var parseStructureFile = require('./parseStructureFile');
-var Readme = require('../models/readme');
+const parseStructureFile = require('./parseStructureFile');
+const Readme = require('../models/readme');
 
-var error = require('../utils/error');
+const error = require('../utils/error');
 
 /**
     Parse readme from book
@@ -10,7 +10,7 @@ var error = require('../utils/error');
     @return {Promise<Book>}
 */
 function parseReadme(book) {
-    var logger = book.getLogger();
+    const logger = book.getLogger();
 
     return parseStructureFile(book, 'readme')
     .spread(function(file, result) {
@@ -20,7 +20,7 @@ function parseReadme(book) {
 
         logger.debug.ln('readme found at', file.getPath());
 
-        var readme = Readme.create(file, result);
+        const readme = Readme.create(file, result);
         return book.set('readme', readme);
     });
 }
diff --git a/packages/gitbook/lib/parse/parseStructureFile.js b/packages/gitbook/src/parse/parseStructureFile.js
index 718f731..951da96 100644
--- a/packages/gitbook/lib/parse/parseStructureFile.js
+++ b/packages/gitbook/src/parse/parseStructureFile.js
@@ -1,6 +1,6 @@
-var Promise = require('../utils/promise');
-var error = require('../utils/error');
-var lookupStructureFile = require('./lookupStructureFile');
+const Promise = require('../utils/promise');
+const error = require('../utils/error');
+const lookupStructureFile = require('./lookupStructureFile');
 
 /**
     Parse a ParsableFile using a specific method
@@ -11,8 +11,8 @@ var lookupStructureFile = require('./lookupStructureFile');
     @return {Promise<Array<String, List|Map>>}
 */
 function parseFile(fs, file, type) {
-    var filepath = file.getPath();
-    var parser = file.getParser();
+    const filepath = file.getPath();
+    const parser = file.getParser();
 
     if (!parser) {
         return Promise.reject(
@@ -54,7 +54,7 @@ function parseFile(fs, file, type) {
     @return {Promise<List|Map>}
 */
 function parseStructureFile(book, type) {
-    var fs = book.getContentFS();
+    const fs = book.getContentFS();
 
     return lookupStructureFile(book, type)
     .then(function(file) {
diff --git a/packages/gitbook/lib/parse/parseSummary.js b/packages/gitbook/src/parse/parseSummary.js
index 2c1e3b3..9488341 100644
--- a/packages/gitbook/lib/parse/parseSummary.js
+++ b/packages/gitbook/src/parse/parseSummary.js
@@ -1,6 +1,6 @@
-var parseStructureFile = require('./parseStructureFile');
-var Summary = require('../models/summary');
-var SummaryModifier = require('../modifiers').Summary;
+const parseStructureFile = require('./parseStructureFile');
+const Summary = require('../models/summary');
+const SummaryModifier = require('../modifiers').Summary;
 
 /**
     Parse summary in a book, the summary can only be parsed
@@ -10,13 +10,13 @@ var SummaryModifier = require('../modifiers').Summary;
     @return {Promise<Book>}
 */
 function parseSummary(book) {
-    var readme = book.getReadme();
-    var logger = book.getLogger();
-    var readmeFile = readme.getFile();
+    const readme = book.getReadme();
+    const logger = book.getLogger();
+    const readmeFile = readme.getFile();
 
     return parseStructureFile(book, 'summary')
     .spread(function(file, result) {
-        var summary;
+        let summary;
 
         if (!file) {
             logger.warn.ln('no summary file in this book');
@@ -27,7 +27,7 @@ function parseSummary(book) {
         }
 
         // Insert readme as first entry if not in SUMMARY.md
-        var readmeArticle = summary.getByPath(readmeFile.getPath());
+        const readmeArticle = summary.getByPath(readmeFile.getPath());
 
         if (readmeFile.exists() && !readmeArticle) {
             summary = SummaryModifier.unshiftArticle(summary, {
diff --git a/packages/gitbook/lib/parse/validateConfig.js b/packages/gitbook/src/parse/validateConfig.js
index 21294ac..e766fae 100644
--- a/packages/gitbook/lib/parse/validateConfig.js
+++ b/packages/gitbook/src/parse/validateConfig.js
@@ -1,9 +1,9 @@
-var jsonschema = require('jsonschema');
-var jsonSchemaDefaults = require('json-schema-defaults');
+const jsonschema = require('jsonschema');
+const jsonSchemaDefaults = require('json-schema-defaults');
 
-var schema = require('../constants/configSchema');
-var error = require('../utils/error');
-var mergeDefaults = require('../utils/mergeDefaults');
+const schema = require('../constants/configSchema');
+const error = require('../utils/error');
+const mergeDefaults = require('../utils/mergeDefaults');
 
 /**
     Validate a book.json content
@@ -13,8 +13,8 @@ var mergeDefaults = require('../utils/mergeDefaults');
     @return {Object}
 */
 function validateConfig(bookJson) {
-    var v = new jsonschema.Validator();
-    var result = v.validate(bookJson, schema, {
+    const v = new jsonschema.Validator();
+    const result = v.validate(bookJson, schema, {
         propertyName: 'config'
     });
 
@@ -24,7 +24,7 @@ function validateConfig(bookJson) {
     }
 
     // Insert default values
-    var defaults = jsonSchemaDefaults(schema);
+    const defaults = jsonSchemaDefaults(schema);
     return mergeDefaults(bookJson, defaults);
 }
 
diff --git a/packages/gitbook/lib/parse/walkSummary.js b/packages/gitbook/src/parse/walkSummary.js
index 0117752..47feb1f 100644
--- a/packages/gitbook/lib/parse/walkSummary.js
+++ b/packages/gitbook/src/parse/walkSummary.js
@@ -1,4 +1,4 @@
-var Promise = require('../utils/promise');
+const Promise = require('../utils/promise');
 
 /**
     Walk over a list of articles
@@ -24,7 +24,7 @@ function walkArticles(articles, fn) {
     @return {Promise}
 */
 function walkSummary(summary, fn) {
-    var parts = summary.getParts();
+    const parts = summary.getParts();
 
     return Promise.forEach(parts, function(part) {
         return walkArticles(part.getArticles(), fn);
diff --git a/packages/gitbook/lib/parsers.js b/packages/gitbook/src/parsers.js
index 70e44f4..62c3776 100644
--- a/packages/gitbook/lib/parsers.js
+++ b/packages/gitbook/src/parsers.js
@@ -1,15 +1,15 @@
-var path = require('path');
-var Immutable = require('immutable');
+const path = require('path');
+const Immutable = require('immutable');
 
-var markdownParser = require('gitbook-markdown');
-var asciidocParser = require('gitbook-asciidoc');
+const markdownParser = require('gitbook-markdown');
+const asciidocParser = require('gitbook-asciidoc');
 
-var EXTENSIONS_MARKDOWN = require('./constants/extsMarkdown');
-var EXTENSIONS_ASCIIDOC = require('./constants/extsAsciidoc');
-var Parser = require('./models/parser');
+const EXTENSIONS_MARKDOWN = require('./constants/extsMarkdown');
+const EXTENSIONS_ASCIIDOC = require('./constants/extsAsciidoc');
+const Parser = require('./models/parser');
 
 // This list is ordered by priority of parsers to use
-var parsers = Immutable.List([
+const parsers = Immutable.List([
     Parser.create('markdown', EXTENSIONS_MARKDOWN, markdownParser),
     Parser.create('asciidoc', EXTENSIONS_ASCIIDOC, asciidocParser)
 ]);
@@ -49,14 +49,14 @@ function getParserForFile(filename) {
 }
 
 // List all parsable extensions
-var extensions = parsers
+const extensions = parsers
     .map(function(parser) {
         return parser.getExtensions();
     })
     .flatten();
 
 module.exports = {
-    extensions: extensions,
+    extensions,
     get: getParser,
     getByExt: getParserByExt,
     getForFile: getParserForFile
diff --git a/packages/gitbook/lib/plugins/__tests__/findForBook.js b/packages/gitbook/src/plugins/__tests__/findForBook.js
index d8af2e9..41df77e 100644
--- a/packages/gitbook/lib/plugins/__tests__/findForBook.js
+++ b/packages/gitbook/src/plugins/__tests__/findForBook.js
@@ -1,14 +1,14 @@
-var path = require('path');
+const path = require('path');
 
-var Book = require('../../models/book');
-var createNodeFS = require('../../fs/node');
-var findForBook = require('../findForBook');
+const Book = require('../../models/book');
+const createNodeFS = require('../../fs/node');
+const findForBook = require('../findForBook');
 
 describe('findForBook', function() {
-    var fs = createNodeFS(
+    const fs = createNodeFS(
         path.resolve(__dirname, '../../..')
     );
-    var book = Book.createForFS(fs);
+    const book = Book.createForFS(fs);
 
     it('should list default plugins', function() {
         return findForBook(book)
diff --git a/packages/gitbook/lib/plugins/__tests__/findInstalled.js b/packages/gitbook/src/plugins/__tests__/findInstalled.js
index 9377190..dcaa62b 100644
--- a/packages/gitbook/lib/plugins/__tests__/findInstalled.js
+++ b/packages/gitbook/src/plugins/__tests__/findInstalled.js
@@ -1,13 +1,13 @@
-var path = require('path');
-var Immutable = require('immutable');
+const path = require('path');
+const Immutable = require('immutable');
 
 describe('findInstalled', function() {
-    var findInstalled = require('../findInstalled');
+    const findInstalled = require('../findInstalled');
 
     it('must list default plugins for gitbook directory', function() {
         // Read gitbook-plugins from package.json
-        var pkg = require(path.resolve(__dirname, '../../../package.json'));
-        var gitbookPlugins = Immutable.Seq(pkg.dependencies)
+        const pkg = require(path.resolve(__dirname, '../../../package.json'));
+        const gitbookPlugins = Immutable.Seq(pkg.dependencies)
             .filter(function(v, k) {
                 return k.indexOf('gitbook-plugin') === 0;
             })
diff --git a/packages/gitbook/src/plugins/__tests__/installPlugin.js b/packages/gitbook/src/plugins/__tests__/installPlugin.js
new file mode 100644
index 0000000..1a8debe
--- /dev/null
+++ b/packages/gitbook/src/plugins/__tests__/installPlugin.js
@@ -0,0 +1,29 @@
+const path = require('path');
+
+const PluginDependency = require('../../models/pluginDependency');
+const Book = require('../../models/book');
+const NodeFS = require('../../fs/node');
+const installPlugin = require('../installPlugin');
+
+const Parse = require('../../parse');
+
+describe('installPlugin', function() {
+    let book;
+
+    this.timeout(30000);
+
+    before(function() {
+        const fs = NodeFS(path.resolve(__dirname, '../../../'));
+        const baseBook = Book.createForFS(fs);
+
+        return Parse.parseConfig(baseBook)
+        .then(function(_book) {
+            book = _book;
+        });
+    });
+
+    it('must install a plugin from NPM', function() {
+        const dep = PluginDependency.createFromString('ga');
+        return installPlugin(book, dep);
+    });
+});
diff --git a/packages/gitbook/lib/plugins/__tests__/installPlugins.js b/packages/gitbook/src/plugins/__tests__/installPlugins.js
index 1a66f90..b6bb1f4 100644
--- a/packages/gitbook/lib/plugins/__tests__/installPlugins.js
+++ b/packages/gitbook/src/plugins/__tests__/installPlugins.js
@@ -1,19 +1,19 @@
-var path = require('path');
+const path = require('path');
 
-var Book = require('../../models/book');
-var NodeFS = require('../../fs/node');
-var installPlugins = require('../installPlugins');
+const Book = require('../../models/book');
+const NodeFS = require('../../fs/node');
+const installPlugins = require('../installPlugins');
 
-var Parse = require('../../parse');
+const Parse = require('../../parse');
 
 describe('installPlugins', function() {
-    var book;
+    let book;
 
     this.timeout(30000);
 
     before(function() {
-        var fs = NodeFS(path.resolve(__dirname, '../../../'));
-        var baseBook = Book.createForFS(fs);
+        const fs = NodeFS(path.resolve(__dirname, '../../../'));
+        const baseBook = Book.createForFS(fs);
 
         return Parse.parseConfig(baseBook)
         .then(function(_book) {
diff --git a/packages/gitbook/lib/plugins/__tests__/listDependencies.js b/packages/gitbook/src/plugins/__tests__/listDependencies.js
index 940faba..d30e46c 100644
--- a/packages/gitbook/lib/plugins/__tests__/listDependencies.js
+++ b/packages/gitbook/src/plugins/__tests__/listDependencies.js
@@ -1,12 +1,12 @@
-var PluginDependency = require('../../models/pluginDependency');
-var listDependencies = require('../listDependencies');
-var toNames = require('../toNames');
+const PluginDependency = require('../../models/pluginDependency');
+const listDependencies = require('../listDependencies');
+const toNames = require('../toNames');
 
 describe('listDependencies', function() {
     it('must list default', function() {
-        var deps = PluginDependency.listFromString('ga,great');
-        var plugins = listDependencies(deps);
-        var names = toNames(plugins);
+        const deps = PluginDependency.listFromString('ga,great');
+        const plugins = listDependencies(deps);
+        const names = toNames(plugins);
 
         expect(names).toEqual([
             'ga', 'great',
@@ -15,9 +15,9 @@ describe('listDependencies', function() {
     });
 
     it('must list from array with -', function() {
-        var deps = PluginDependency.listFromString('ga,-great');
-        var plugins = listDependencies(deps);
-        var names = toNames(plugins);
+        const deps = PluginDependency.listFromString('ga,-great');
+        const plugins = listDependencies(deps);
+        const names = toNames(plugins);
 
         expect(names).toEqual([
             'ga',
@@ -26,9 +26,9 @@ describe('listDependencies', function() {
     });
 
     it('must remove default plugins using -', function() {
-        var deps = PluginDependency.listFromString('ga,-search');
-        var plugins = listDependencies(deps);
-        var names = toNames(plugins);
+        const deps = PluginDependency.listFromString('ga,-search');
+        const plugins = listDependencies(deps);
+        const names = toNames(plugins);
 
         expect(names).toEqual([
             'ga',
diff --git a/packages/gitbook/lib/plugins/__tests__/locateRootFolder.js b/packages/gitbook/src/plugins/__tests__/locateRootFolder.js
index bb414a3..54e095b 100644
--- a/packages/gitbook/lib/plugins/__tests__/locateRootFolder.js
+++ b/packages/gitbook/src/plugins/__tests__/locateRootFolder.js
@@ -1,5 +1,5 @@
-var path = require('path');
-var locateRootFolder = require('../locateRootFolder');
+const path = require('path');
+const locateRootFolder = require('../locateRootFolder');
 
 describe('locateRootFolder', function() {
     it('should correctly resolve the node_modules for gitbook', function() {
diff --git a/packages/gitbook/lib/plugins/__tests__/resolveVersion.js b/packages/gitbook/src/plugins/__tests__/resolveVersion.js
index 1877c9e..949d078 100644
--- a/packages/gitbook/lib/plugins/__tests__/resolveVersion.js
+++ b/packages/gitbook/src/plugins/__tests__/resolveVersion.js
@@ -1,9 +1,9 @@
-var PluginDependency = require('../../models/pluginDependency');
-var resolveVersion = require('../resolveVersion');
+const PluginDependency = require('../../models/pluginDependency');
+const resolveVersion = require('../resolveVersion');
 
 describe('resolveVersion', function() {
     it('must skip resolving and return non-semver versions', function() {
-        var plugin = PluginDependency.createFromString('ga@git+ssh://samy@github.com/GitbookIO/plugin-ga.git');
+        const plugin = PluginDependency.createFromString('ga@git+ssh://samy@github.com/GitbookIO/plugin-ga.git');
 
         return resolveVersion(plugin)
         .then(function(version) {
@@ -12,7 +12,7 @@ describe('resolveVersion', function() {
     });
 
     it('must resolve a normal plugin dependency', function() {
-        var plugin = PluginDependency.createFromString('ga@>0.9.0 < 1.0.1');
+        const plugin = PluginDependency.createFromString('ga@>0.9.0 < 1.0.1');
 
         return resolveVersion(plugin)
         .then(function(version) {
diff --git a/packages/gitbook/lib/plugins/__tests__/sortDependencies.js b/packages/gitbook/src/plugins/__tests__/sortDependencies.js
index 87df477..a08d59d 100644
--- a/packages/gitbook/lib/plugins/__tests__/sortDependencies.js
+++ b/packages/gitbook/src/plugins/__tests__/sortDependencies.js
@@ -1,17 +1,17 @@
-var PluginDependency = require('../../models/pluginDependency');
-var sortDependencies = require('../sortDependencies');
-var toNames = require('../toNames');
+const PluginDependency = require('../../models/pluginDependency');
+const sortDependencies = require('../sortDependencies');
+const toNames = require('../toNames');
 
 describe('sortDependencies', function() {
     it('must load themes after plugins', function() {
-        var allPlugins = PluginDependency.listFromArray([
+        const allPlugins = PluginDependency.listFromArray([
             'hello',
             'theme-test',
             'world'
         ]);
 
-        var sorted = sortDependencies(allPlugins);
-        var names = toNames(sorted);
+        const sorted = sortDependencies(allPlugins);
+        const names = toNames(sorted);
 
         expect(names).toEqual([
             'hello',
@@ -21,15 +21,15 @@ describe('sortDependencies', function() {
     });
 
     it('must keep order of themes', function() {
-        var allPlugins = PluginDependency.listFromArray([
+        const allPlugins = PluginDependency.listFromArray([
             'theme-test',
             'theme-test1',
             'hello',
             'theme-test2',
             'world'
         ]);
-        var sorted = sortDependencies(allPlugins);
-        var names = toNames(sorted);
+        const sorted = sortDependencies(allPlugins);
+        const names = toNames(sorted);
 
         expect(names).toEqual([
             'hello',
@@ -39,4 +39,4 @@ describe('sortDependencies', function() {
             'theme-test2'
         ]);
     });
-});
\ No newline at end of file
+});
diff --git a/packages/gitbook/lib/plugins/__tests__/validatePlugin.js b/packages/gitbook/src/plugins/__tests__/validatePlugin.js
index 635423c..a2bd23b 100644
--- a/packages/gitbook/lib/plugins/__tests__/validatePlugin.js
+++ b/packages/gitbook/src/plugins/__tests__/validatePlugin.js
@@ -1,10 +1,10 @@
-var Promise = require('../../utils/promise');
-var Plugin = require('../../models/plugin');
-var validatePlugin = require('../validatePlugin');
+const Promise = require('../../utils/promise');
+const Plugin = require('../../models/plugin');
+const validatePlugin = require('../validatePlugin');
 
 describe('validatePlugin', function() {
     it('must not validate a not loaded plugin', function() {
-        var plugin = Plugin.createFromString('test');
+        const plugin = Plugin.createFromString('test');
 
         return validatePlugin(plugin)
         .then(function() {
diff --git a/packages/gitbook/lib/plugins/findForBook.js b/packages/gitbook/src/plugins/findForBook.js
index be2ad9f..b72d526 100644
--- a/packages/gitbook/lib/plugins/findForBook.js
+++ b/packages/gitbook/src/plugins/findForBook.js
@@ -1,9 +1,9 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var Promise = require('../utils/promise');
-var timing = require('../utils/timing');
-var findInstalled = require('./findInstalled');
-var locateRootFolder = require('./locateRootFolder');
+const Promise = require('../utils/promise');
+const timing = require('../utils/timing');
+const findInstalled = require('./findInstalled');
+const locateRootFolder = require('./locateRootFolder');
 
 /**
  * List all plugins installed in a book
diff --git a/packages/gitbook/lib/plugins/findInstalled.js b/packages/gitbook/src/plugins/findInstalled.js
index 06cc6c4..15556b6 100644
--- a/packages/gitbook/lib/plugins/findInstalled.js
+++ b/packages/gitbook/src/plugins/findInstalled.js
@@ -1,11 +1,11 @@
-var readInstalled = require('read-installed');
-var Immutable = require('immutable');
-var path = require('path');
+const readInstalled = require('read-installed');
+const Immutable = require('immutable');
+const path = require('path');
 
-var Promise = require('../utils/promise');
-var fs = require('../utils/fs');
-var Plugin = require('../models/plugin');
-var PREFIX = require('../constants/pluginPrefix');
+const Promise = require('../utils/promise');
+const fs = require('../utils/fs');
+const Plugin = require('../models/plugin');
+const PREFIX = require('../constants/pluginPrefix');
 
 /**
  * Validate if a package name is a GitBook plugin
@@ -24,33 +24,33 @@ function validateId(name) {
  * @return {OrderedMap<String:Plugin>}
  */
 function findInstalled(folder) {
-    var options = {
+    const options = {
         dev: false,
-        log: function() {},
+        log() {},
         depth: 4
     };
-    var results = Immutable.OrderedMap();
+    let results = Immutable.OrderedMap();
 
     function onPackage(pkg, parent) {
         if (!pkg.name) return;
 
-        var name = pkg.name;
-        var version = pkg.version;
-        var pkgPath = pkg.realPath;
-        var depth = pkg.depth;
-        var dependencies = pkg.dependencies;
+        const name = pkg.name;
+        const version = pkg.version;
+        const pkgPath = pkg.realPath;
+        const depth = pkg.depth;
+        const dependencies = pkg.dependencies;
 
-        var pluginName = name.slice(PREFIX.length);
+        const pluginName = name.slice(PREFIX.length);
 
-        if (!validateId(name)){
+        if (!validateId(name)) {
             if (parent) return;
         } else {
             results = results.set(pluginName, Plugin({
                 name: pluginName,
-                version: version,
+                version,
                 path: pkgPath,
-                depth: depth,
-                parent: parent
+                depth,
+                parent
             }));
         }
 
@@ -60,7 +60,7 @@ function findInstalled(folder) {
     }
 
     // Search for gitbook-plugins in node_modules folder
-    var node_modules = path.join(folder, 'node_modules');
+    const node_modules = path.join(folder, 'node_modules');
 
     // List all folders in node_modules
     return fs.readdir(node_modules)
@@ -75,7 +75,7 @@ function findInstalled(folder) {
             }
 
             // Read gitbook-plugin package details
-            var module_folder = path.join(node_modules, module);
+            const module_folder = path.join(node_modules, module);
             return Promise.nfcall(readInstalled, module_folder, options)
             .then(function(data) {
                 onPackage(data);
diff --git a/packages/gitbook/lib/plugins/index.js b/packages/gitbook/src/plugins/index.js
index 607a7f1..607a7f1 100644
--- a/packages/gitbook/lib/plugins/index.js
+++ b/packages/gitbook/src/plugins/index.js
diff --git a/packages/gitbook/lib/plugins/installPlugin.js b/packages/gitbook/src/plugins/installPlugin.js
index 37852df..edf4dc5 100644
--- a/packages/gitbook/lib/plugins/installPlugin.js
+++ b/packages/gitbook/src/plugins/installPlugin.js
@@ -1,7 +1,7 @@
-var npmi = require('npmi');
+const npmi = require('npmi');
 
-var Promise = require('../utils/promise');
-var resolveVersion = require('./resolveVersion');
+const Promise = require('../utils/promise');
+const resolveVersion = require('./resolveVersion');
 
 /**
     Install a plugin for a book
@@ -11,11 +11,11 @@ var resolveVersion = require('./resolveVersion');
     @return {Promise}
 */
 function installPlugin(book, plugin) {
-    var logger = book.getLogger();
+    const logger = book.getLogger();
 
-    var installFolder = book.getRoot();
-    var name = plugin.getName();
-    var requirement = plugin.getVersion();
+    const installFolder = book.getRoot();
+    const name = plugin.getName();
+    const requirement = plugin.getVersion();
 
     logger.info.ln('');
     logger.info.ln('installing plugin "' + name + '"');
@@ -27,10 +27,10 @@ function installPlugin(book, plugin) {
             throw new Error('Found no satisfactory version for plugin "' + name + '" with requirement "' + requirement + '"');
         }
 
-        logger.info.ln('install plugin "' + name +'" (' + requirement + ') from NPM with version', version);
+        logger.info.ln('install plugin "' + name + '" (' + requirement + ') from NPM with version', version);
         return Promise.nfcall(npmi, {
             'name': plugin.getNpmID(),
-            'version': version,
+            version,
             'path': installFolder,
             'npmLoad': {
                 'loglevel': 'silent',
diff --git a/packages/gitbook/lib/plugins/installPlugins.js b/packages/gitbook/src/plugins/installPlugins.js
index 307c41e..8c36c92 100644
--- a/packages/gitbook/lib/plugins/installPlugins.js
+++ b/packages/gitbook/src/plugins/installPlugins.js
@@ -1,8 +1,8 @@
-var npmi = require('npmi');
+const npmi = require('npmi');
 
-var DEFAULT_PLUGINS = require('../constants/defaultPlugins');
-var Promise = require('../utils/promise');
-var installPlugin = require('./installPlugin');
+const DEFAULT_PLUGINS = require('../constants/defaultPlugins');
+const Promise = require('../utils/promise');
+const installPlugin = require('./installPlugin');
 
 /**
     Install plugin requirements for a book
@@ -11,14 +11,14 @@ var installPlugin = require('./installPlugin');
     @return {Promise<Number>}
 */
 function installPlugins(book) {
-    var logger = book.getLogger();
-    var config = book.getConfig();
-    var plugins = config.getPluginDependencies();
+    const logger = book.getLogger();
+    const config = book.getConfig();
+    let plugins = config.getPluginDependencies();
 
     // Remove default plugins
     // (only if version is same as installed)
     plugins = plugins.filterNot(function(plugin) {
-        var dependency = DEFAULT_PLUGINS.find(function(dep) {
+        const dependency = DEFAULT_PLUGINS.find(function(dep) {
             return dep.getName() === plugin.getName();
         });
 
diff --git a/packages/gitbook/lib/plugins/listBlocks.js b/packages/gitbook/src/plugins/listBlocks.js
index 3ac28af..991b386 100644
--- a/packages/gitbook/lib/plugins/listBlocks.js
+++ b/packages/gitbook/src/plugins/listBlocks.js
@@ -1,4 +1,4 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
 /**
     List blocks from a list of plugins
@@ -10,7 +10,7 @@ function listBlocks(plugins) {
     return plugins
         .reverse()
         .reduce(function(result, plugin) {
-            var blocks = plugin.getBlocks();
+            const blocks = plugin.getBlocks();
             return result.merge(blocks);
         }, Immutable.Map());
 }
diff --git a/packages/gitbook/lib/plugins/listDependencies.js b/packages/gitbook/src/plugins/listDependencies.js
index d52eaa9..3930ae7 100644
--- a/packages/gitbook/lib/plugins/listDependencies.js
+++ b/packages/gitbook/src/plugins/listDependencies.js
@@ -1,5 +1,5 @@
-var DEFAULT_PLUGINS = require('../constants/defaultPlugins');
-var sortDependencies = require('./sortDependencies');
+const DEFAULT_PLUGINS = require('../constants/defaultPlugins');
+const sortDependencies = require('./sortDependencies');
 
 /**
  * List all dependencies for a book, including default plugins.
@@ -10,7 +10,7 @@ var sortDependencies = require('./sortDependencies');
  */
 function listDependencies(deps) {
     // Extract list of plugins to disable (starting with -)
-    var toRemove = deps
+    const toRemove = deps
         .filter(function(plugin) {
             return !plugin.isEnabled();
         })
diff --git a/packages/gitbook/lib/plugins/listDepsForBook.js b/packages/gitbook/src/plugins/listDepsForBook.js
index 196e3aa..b173572 100644
--- a/packages/gitbook/lib/plugins/listDepsForBook.js
+++ b/packages/gitbook/src/plugins/listDepsForBook.js
@@ -1,4 +1,4 @@
-var listDependencies = require('./listDependencies');
+const listDependencies = require('./listDependencies');
 
 /**
  * List all plugin requirements for a book.
@@ -9,8 +9,8 @@ var listDependencies = require('./listDependencies');
  * @return {List<PluginDependency>}
  */
 function listDepsForBook(book) {
-    var config = book.getConfig();
-    var plugins = config.getPluginDependencies();
+    const config = book.getConfig();
+    const plugins = config.getPluginDependencies();
 
     return listDependencies(plugins);
 }
diff --git a/packages/gitbook/lib/plugins/listFilters.js b/packages/gitbook/src/plugins/listFilters.js
index 4d8a471..edf6c0d 100644
--- a/packages/gitbook/lib/plugins/listFilters.js
+++ b/packages/gitbook/src/plugins/listFilters.js
@@ -1,4 +1,4 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
 /**
     List filters from a list of plugins
diff --git a/packages/gitbook/lib/plugins/listResources.js b/packages/gitbook/src/plugins/listResources.js
index fe31b5a..df50097 100644
--- a/packages/gitbook/lib/plugins/listResources.js
+++ b/packages/gitbook/src/plugins/listResources.js
@@ -1,8 +1,8 @@
-var Immutable = require('immutable');
-var path = require('path');
+const Immutable = require('immutable');
+const path = require('path');
 
-var LocationUtils = require('../utils/location');
-var PLUGIN_RESOURCES = require('../constants/pluginResources');
+const LocationUtils = require('../utils/location');
+const PLUGIN_RESOURCES = require('../constants/pluginResources');
 
 /**
     List all resources from a list of plugins
@@ -13,14 +13,14 @@ var PLUGIN_RESOURCES = require('../constants/pluginResources');
 */
 function listResources(plugins, resources) {
     return plugins.reduce(function(result, plugin) {
-        var npmId           = plugin.getNpmID();
-        var pluginResources = resources.get(plugin.getName());
+        const npmId           = plugin.getNpmID();
+        const pluginResources = resources.get(plugin.getName());
 
         PLUGIN_RESOURCES.forEach(function(resourceType) {
-            var assets = pluginResources.get(resourceType);
+            let assets = pluginResources.get(resourceType);
             if (!assets) return;
 
-            var list = result.get(resourceType) || Immutable.List();
+            let list = result.get(resourceType) || Immutable.List();
 
             assets = assets.map(function(assetFile) {
                 if (LocationUtils.isExternal(assetFile)) {
diff --git a/packages/gitbook/lib/plugins/loadForBook.js b/packages/gitbook/src/plugins/loadForBook.js
index 757677e..0baa78e 100644
--- a/packages/gitbook/lib/plugins/loadForBook.js
+++ b/packages/gitbook/src/plugins/loadForBook.js
@@ -1,9 +1,9 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var Promise = require('../utils/promise');
-var listDepsForBook = require('./listDepsForBook');
-var findForBook = require('./findForBook');
-var loadPlugin = require('./loadPlugin');
+const Promise = require('../utils/promise');
+const listDepsForBook = require('./listDepsForBook');
+const findForBook = require('./findForBook');
+const loadPlugin = require('./loadPlugin');
 
 
 /**
@@ -13,21 +13,21 @@ var loadPlugin = require('./loadPlugin');
  * @return {Promise<Map<String:Plugin>}
  */
 function loadForBook(book) {
-    var logger = book.getLogger();
+    const logger = book.getLogger();
 
     // List the dependencies
-    var requirements = listDepsForBook(book);
+    const requirements = listDepsForBook(book);
 
     // List all plugins installed in the book
     return findForBook(book)
     .then(function(installedMap) {
-        var missing = [];
-        var plugins = requirements.reduce(function(result, dep) {
-            var name = dep.getName();
-            var installed = installedMap.get(name);
+        const missing = [];
+        let plugins = requirements.reduce(function(result, dep) {
+            const name = dep.getName();
+            const installed = installedMap.get(name);
 
             if (installed) {
-                var deps = installedMap
+                const deps = installedMap
                     .filter(function(plugin) {
                         return plugin.getParent() === name;
                     })
diff --git a/packages/gitbook/lib/plugins/loadPlugin.js b/packages/gitbook/src/plugins/loadPlugin.js
index 9ed83a1..4a349e2 100644
--- a/packages/gitbook/lib/plugins/loadPlugin.js
+++ b/packages/gitbook/src/plugins/loadPlugin.js
@@ -1,12 +1,12 @@
-var path = require('path');
-var resolve = require('resolve');
-var Immutable = require('immutable');
+const path = require('path');
+const resolve = require('resolve');
+const Immutable = require('immutable');
 
-var Promise = require('../utils/promise');
-var error = require('../utils/error');
-var timing = require('../utils/timing');
+const Promise = require('../utils/promise');
+const error = require('../utils/error');
+const timing = require('../utils/timing');
 
-var validatePlugin = require('./validatePlugin');
+const validatePlugin = require('./validatePlugin');
 
 // Return true if an error is a "module not found"
 // Wait on https://github.com/substack/node-resolve/pull/81 to be merged
@@ -23,21 +23,21 @@ function isModuleNotFound(err) {
     @return {Promise<Plugin>}
 */
 function loadPlugin(book, plugin) {
-    var logger = book.getLogger();
+    const logger = book.getLogger();
 
-    var name = plugin.getName();
-    var pkgPath = plugin.getPath();
+    const name = plugin.getName();
+    let pkgPath = plugin.getPath();
 
     // Try loading plugins from different location
-    var p = Promise()
+    let p = Promise()
     .then(function() {
-        var packageContent;
-        var packageMain;
-        var content;
+        let packageContent;
+        let packageMain;
+        let content;
 
         // Locate plugin and load package.json
         try {
-            var res = resolve.sync('./package.json', { basedir: pkgPath });
+            const res = resolve.sync('./package.json', { basedir: pkgPath });
 
             pkgPath = path.dirname(res);
             packageContent = require(res);
@@ -52,7 +52,7 @@ function loadPlugin(book, plugin) {
 
         // Locate the main package
         try {
-            var indexJs = path.normalize(packageContent.main || 'index.js');
+            const indexJs = path.normalize(packageContent.main || 'index.js');
             packageMain = resolve.sync('./' + indexJs, { basedir: pkgPath });
         } catch (err) {
             if (!isModuleNotFound(err)) throw err;
@@ -63,7 +63,7 @@ function loadPlugin(book, plugin) {
         if (packageMain) {
             try {
                 content = require(packageMain);
-            } catch(err) {
+            } catch (err) {
                 throw new error.PluginError(err, {
                     plugin: name
                 });
diff --git a/packages/gitbook/src/plugins/locateRootFolder.js b/packages/gitbook/src/plugins/locateRootFolder.js
new file mode 100644
index 0000000..64e06a8
--- /dev/null
+++ b/packages/gitbook/src/plugins/locateRootFolder.js
@@ -0,0 +1,22 @@
+const path = require('path');
+const resolve = require('resolve');
+
+const DEFAULT_PLUGINS = require('../constants/defaultPlugins');
+
+/**
+ * Resolve the root folder containing for node_modules
+ * since gitbook can be used as a library and dependency can be flattened.
+ *
+ * @return {String} folderPath
+ */
+function locateRootFolder() {
+    const firstDefaultPlugin = DEFAULT_PLUGINS.first();
+    const pluginPath = resolve.sync(firstDefaultPlugin.getNpmID() + '/package.json', {
+        basedir: __dirname
+    });
+    const nodeModules = path.resolve(pluginPath, '../../..');
+
+    return nodeModules;
+}
+
+module.exports = locateRootFolder;
diff --git a/packages/gitbook/lib/plugins/resolveVersion.js b/packages/gitbook/src/plugins/resolveVersion.js
index 61aef8d..07b771e 100644
--- a/packages/gitbook/lib/plugins/resolveVersion.js
+++ b/packages/gitbook/src/plugins/resolveVersion.js
@@ -1,12 +1,12 @@
-var npm = require('npm');
-var semver = require('semver');
-var Immutable = require('immutable');
+const npm = require('npm');
+const semver = require('semver');
+const Immutable = require('immutable');
 
-var Promise = require('../utils/promise');
-var Plugin = require('../models/plugin');
-var gitbook = require('../gitbook');
+const Promise = require('../utils/promise');
+const Plugin = require('../models/plugin');
+const gitbook = require('../gitbook');
 
-var npmIsReady;
+let npmIsReady;
 
 /**
     Initialize and prepare NPM
@@ -31,8 +31,8 @@ function initNPM() {
     @return {Promise<String>}
 */
 function resolveVersion(plugin) {
-    var npmId = Plugin.nameToNpmID(plugin.getName());
-    var requiredVersion = plugin.getVersion();
+    const npmId = Plugin.nameToNpmID(plugin.getName());
+    const requiredVersion = plugin.getVersion();
 
     if (plugin.isGitDependency()) {
         return Promise.resolve(requiredVersion);
@@ -45,7 +45,7 @@ function resolveVersion(plugin) {
     .then(function(versions) {
         versions = Immutable.Map(versions).entrySeq();
 
-        var result = versions
+        const result = versions
             .map(function(entry) {
                 return {
                     version: entry[0],
@@ -56,7 +56,7 @@ function resolveVersion(plugin) {
                 return v.gitbook && gitbook.satisfies(v.gitbook);
             })
             .sort(function(v1, v2) {
-                return semver.lt(v1.version, v2.version)? 1 : -1;
+                return semver.lt(v1.version, v2.version) ? 1 : -1;
             })
             .get(0);
 
diff --git a/packages/gitbook/lib/plugins/sortDependencies.js b/packages/gitbook/src/plugins/sortDependencies.js
index 7f10095..2adfa20 100644
--- a/packages/gitbook/lib/plugins/sortDependencies.js
+++ b/packages/gitbook/src/plugins/sortDependencies.js
@@ -1,9 +1,9 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var THEME_PREFIX = require('../constants/themePrefix');
+const THEME_PREFIX = require('../constants/themePrefix');
 
-var TYPE_PLUGIN = 'plugin';
-var TYPE_THEME  = 'theme';
+const TYPE_PLUGIN = 'plugin';
+const TYPE_THEME  = 'theme';
 
 
 /**
@@ -12,7 +12,7 @@ var TYPE_THEME  = 'theme';
  * @return {String}
  */
 function pluginType(plugin) {
-    var name = plugin.getName();
+    const name = plugin.getName();
     return (name && name.indexOf(THEME_PREFIX) === 0) ? TYPE_THEME : TYPE_PLUGIN;
 }
 
@@ -25,10 +25,10 @@ function pluginType(plugin) {
  * @return {List<PluginDependency>}
  */
 function sortDependencies(plugins) {
-    var byTypes = plugins.groupBy(pluginType);
+    const byTypes = plugins.groupBy(pluginType);
 
     return byTypes.get(TYPE_PLUGIN, Immutable.List())
         .concat(byTypes.get(TYPE_THEME, Immutable.List()));
 }
 
-module.exports = sortDependencies;
\ No newline at end of file
+module.exports = sortDependencies;
diff --git a/packages/gitbook/lib/plugins/toNames.js b/packages/gitbook/src/plugins/toNames.js
index ad0dd8f..ad0dd8f 100644
--- a/packages/gitbook/lib/plugins/toNames.js
+++ b/packages/gitbook/src/plugins/toNames.js
diff --git a/packages/gitbook/lib/plugins/validateConfig.js b/packages/gitbook/src/plugins/validateConfig.js
index fab1fef..8e24775 100644
--- a/packages/gitbook/lib/plugins/validateConfig.js
+++ b/packages/gitbook/src/plugins/validateConfig.js
@@ -1,10 +1,10 @@
-var Immutable = require('immutable');
-var jsonschema = require('jsonschema');
-var jsonSchemaDefaults = require('json-schema-defaults');
+const Immutable = require('immutable');
+const jsonschema = require('jsonschema');
+const jsonSchemaDefaults = require('json-schema-defaults');
 
-var Promise = require('../utils/promise');
-var error = require('../utils/error');
-var mergeDefaults = require('../utils/mergeDefaults');
+const Promise = require('../utils/promise');
+const error = require('../utils/error');
+const mergeDefaults = require('../utils/mergeDefaults');
 
 /**
     Validate one plugin for a book and update book's confiration
@@ -14,17 +14,17 @@ var mergeDefaults = require('../utils/mergeDefaults');
     @return {Book}
 */
 function validatePluginConfig(book, plugin) {
-    var config = book.getConfig();
-    var packageInfos = plugin.getPackage();
+    let config = book.getConfig();
+    const packageInfos = plugin.getPackage();
 
-    var configKey = [
+    const configKey = [
         'pluginsConfig',
         plugin.getName()
     ].join('.');
 
-    var pluginConfig = config.getValue(configKey, {}).toJS();
+    let pluginConfig = config.getValue(configKey, {}).toJS();
 
-    var schema = (packageInfos.get('gitbook') || Immutable.Map()).toJS();
+    const schema = (packageInfos.get('gitbook') || Immutable.Map()).toJS();
     if (!schema) return book;
 
     // Normalize schema
@@ -32,8 +32,8 @@ function validatePluginConfig(book, plugin) {
     schema.type = 'object';
 
     // Validate and throw if invalid
-    var v = new jsonschema.Validator();
-    var result = v.validate(pluginConfig, schema, {
+    const v = new jsonschema.Validator();
+    const result = v.validate(pluginConfig, schema, {
         propertyName: configKey
     });
 
@@ -43,7 +43,7 @@ function validatePluginConfig(book, plugin) {
     }
 
     // Insert default values
-    var defaults = jsonSchemaDefaults(schema);
+    const defaults = jsonSchemaDefaults(schema);
     pluginConfig = mergeDefaults(pluginConfig, defaults);
 
 
diff --git a/packages/gitbook/lib/plugins/validatePlugin.js b/packages/gitbook/src/plugins/validatePlugin.js
index 4baa911..f0e96ba 100644
--- a/packages/gitbook/lib/plugins/validatePlugin.js
+++ b/packages/gitbook/src/plugins/validatePlugin.js
@@ -1,6 +1,6 @@
-var gitbook = require('../gitbook');
+const gitbook = require('../gitbook');
 
-var Promise = require('../utils/promise');
+const Promise = require('../utils/promise');
 
 /**
     Validate a plugin
@@ -9,9 +9,9 @@ var Promise = require('../utils/promise');
     @return {Promise<Plugin>}
 */
 function validatePlugin(plugin) {
-    var packageInfos = plugin.getPackage();
+    const packageInfos = plugin.getPackage();
 
-    var isValid = (
+    const isValid = (
         plugin.isLoaded() &&
         packageInfos &&
         packageInfos.get('name') &&
@@ -23,7 +23,7 @@ function validatePlugin(plugin) {
         return Promise.reject(new Error('Error loading plugin "' + plugin.getName() + '" at "' + plugin.getPath() + '"'));
     }
 
-    var engine = packageInfos.get('engines').get('gitbook');
+    const engine = packageInfos.get('engines').get('gitbook');
     if (!gitbook.satisfies(engine)) {
         return Promise.reject(new Error('GitBook doesn\'t satisfy the requirements of this plugin: ' + engine));
     }
diff --git a/packages/gitbook/lib/templating/__tests__/conrefsLoader.js b/packages/gitbook/src/templating/__tests__/conrefsLoader.js
index 196b513..431d0a3 100644
--- a/packages/gitbook/lib/templating/__tests__/conrefsLoader.js
+++ b/packages/gitbook/src/templating/__tests__/conrefsLoader.js
@@ -1,15 +1,15 @@
-var path = require('path');
+const path = require('path');
 
-var TemplateEngine = require('../../models/templateEngine');
-var renderTemplate = require('../render');
-var ConrefsLoader = require('../conrefsLoader');
+const TemplateEngine = require('../../models/templateEngine');
+const renderTemplate = require('../render');
+const ConrefsLoader = require('../conrefsLoader');
 
 describe('ConrefsLoader', function() {
-    var dirName = __dirname + '/';
-    var fileName = path.join(dirName, 'test.md');
+    const dirName = __dirname + '/';
+    const fileName = path.join(dirName, 'test.md');
 
     describe('Git', function() {
-        var engine = TemplateEngine({
+        const engine = TemplateEngine({
             loader: new ConrefsLoader(dirName)
         });
 
@@ -36,7 +36,7 @@ describe('ConrefsLoader', function() {
     });
 
     describe('Local', function() {
-        var engine = TemplateEngine({
+        const engine = TemplateEngine({
             loader: new ConrefsLoader(dirName)
         });
 
@@ -83,7 +83,7 @@ describe('ConrefsLoader', function() {
 
             return 'test-' + source + '-endtest';
         }
-        var engine = TemplateEngine({
+        const engine = TemplateEngine({
             loader: new ConrefsLoader(dirName, transform)
         });
 
diff --git a/packages/gitbook/lib/templating/__tests__/include.md b/packages/gitbook/src/templating/__tests__/include.md
index 5e1c309..5e1c309 100644
--- a/packages/gitbook/lib/templating/__tests__/include.md
+++ b/packages/gitbook/src/templating/__tests__/include.md
diff --git a/packages/gitbook/lib/templating/__tests__/postRender.js b/packages/gitbook/src/templating/__tests__/postRender.js
index 131e29b..ff5bb61 100644
--- a/packages/gitbook/lib/templating/__tests__/postRender.js
+++ b/packages/gitbook/src/templating/__tests__/postRender.js
@@ -1,12 +1,12 @@
-var TemplateEngine = require('../../models/templateEngine');
-var TemplateBlock = require('../../models/templateBlock');
+const TemplateEngine = require('../../models/templateEngine');
+const TemplateBlock = require('../../models/templateBlock');
 
-var renderTemplate = require('../render');
-var postRender = require('../postRender');
+const renderTemplate = require('../render');
+const postRender = require('../postRender');
 
 describe('postRender', function() {
-    var testPost;
-    var engine = TemplateEngine.create({
+    let testPost;
+    const engine = TemplateEngine.create({
         blocks: [
             TemplateBlock.create('lower', function(blk) {
                 return blk.body.toLowerCase();
@@ -14,7 +14,7 @@ describe('postRender', function() {
             TemplateBlock.create('prefix', function(blk) {
                 return {
                     body: '_' + blk.body + '_',
-                    post: function() {
+                    post() {
                         testPost = true;
                     }
                 };
diff --git a/packages/gitbook/lib/templating/__tests__/replaceShortcuts.js b/packages/gitbook/src/templating/__tests__/replaceShortcuts.js
index 216a1c8..cfd18b5 100644
--- a/packages/gitbook/lib/templating/__tests__/replaceShortcuts.js
+++ b/packages/gitbook/src/templating/__tests__/replaceShortcuts.js
@@ -1,10 +1,10 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
-var TemplateBlock = require('../../models/templateBlock');
-var replaceShortcuts = require('../replaceShortcuts');
+const TemplateBlock = require('../../models/templateBlock');
+const replaceShortcuts = require('../replaceShortcuts');
 
 describe('replaceShortcuts', function() {
-    var blocks = Immutable.List([
+    const blocks = Immutable.List([
         TemplateBlock.create('math', {
             shortcuts: {
                 start: '$$',
@@ -15,12 +15,12 @@ describe('replaceShortcuts', function() {
     ]);
 
     it('should correctly replace inline matches by block', function() {
-        var content = replaceShortcuts(blocks, 'test.md', 'Hello $$a = b$$');
+        const content = replaceShortcuts(blocks, 'test.md', 'Hello $$a = b$$');
         expect(content).toBe('Hello {% math %}a = b{% endmath %}');
     });
 
     it('should correctly replace block matches', function() {
-        var content = replaceShortcuts(blocks, 'test.md', 'Hello\n$$\na = b\n$$\n');
+        const content = replaceShortcuts(blocks, 'test.md', 'Hello\n$$\na = b\n$$\n');
         expect(content).toBe('Hello\n{% math %}\na = b\n{% endmath %}\n');
     });
 });
diff --git a/packages/gitbook/lib/templating/conrefsLoader.js b/packages/gitbook/src/templating/conrefsLoader.js
index b3cdb3f..4024a19 100644
--- a/packages/gitbook/lib/templating/conrefsLoader.js
+++ b/packages/gitbook/src/templating/conrefsLoader.js
@@ -1,10 +1,10 @@
-var path = require('path');
-var nunjucks = require('nunjucks');
+const path = require('path');
+const nunjucks = require('nunjucks');
 
-var fs = require('../utils/fs');
-var Git = require('../utils/git');
-var LocationUtils = require('../utils/location');
-var PathUtils = require('../utils/path');
+const fs = require('../utils/fs');
+const Git = require('../utils/git');
+const LocationUtils = require('../utils/location');
+const PathUtils = require('../utils/path');
 
 
 /**
@@ -17,18 +17,18 @@ var PathUtils = require('../utils/path');
  * @param {Function(filePath, source)} transformFn (optional)
  * @param {Logger} logger (optional)
  */
-var ConrefsLoader = nunjucks.Loader.extend({
+const ConrefsLoader = nunjucks.Loader.extend({
     async: true,
 
-    init: function(rootFolder, transformFn, logger) {
+    init(rootFolder, transformFn, logger) {
         this.rootFolder = rootFolder;
         this.transformFn = transformFn;
         this.logger = logger;
         this.git = new Git();
     },
 
-    getSource: function(sourceURL, callback) {
-        var that = this;
+    getSource(sourceURL, callback) {
+        const that = this;
 
         this.git.resolve(sourceURL)
         .then(function(filepath) {
@@ -60,22 +60,22 @@ var ConrefsLoader = nunjucks.Loader.extend({
         .nodeify(callback);
     },
 
-    resolve: function(from, to) {
+    resolve(from, to) {
         // If origin is in the book, we enforce result file to be in the book
         if (PathUtils.isInRoot(this.rootFolder, from)) {
 
             // Path of current template in the rootFolder (not absolute to fs)
-            var fromRelative = path.relative(this.rootFolder, from);
+            const fromRelative = path.relative(this.rootFolder, from);
 
             // Resolve "to" to a filepath relative to rootFolder
-            var href = LocationUtils.toAbsolute(to, path.dirname(fromRelative), '');
+            const href = LocationUtils.toAbsolute(to, path.dirname(fromRelative), '');
 
             // Return absolute path
             return PathUtils.resolveInRoot(this.rootFolder, href);
         }
 
         // If origin is in a git repository, we resolve file in the git repository
-        var gitRoot = this.git.resolveRoot(from);
+        const gitRoot = this.git.resolveRoot(from);
         if (gitRoot) {
             return PathUtils.resolveInRoot(gitRoot, to);
         }
@@ -85,7 +85,7 @@ var ConrefsLoader = nunjucks.Loader.extend({
     },
 
     // Handle all files as relative, so that nunjucks pass responsability to 'resolve'
-    isRelative: function(filename) {
+    isRelative(filename) {
         return LocationUtils.isRelative(filename);
     }
 });
diff --git a/packages/gitbook/lib/templating/index.js b/packages/gitbook/src/templating/index.js
index bd74aca..bd74aca 100644
--- a/packages/gitbook/lib/templating/index.js
+++ b/packages/gitbook/src/templating/index.js
diff --git a/packages/gitbook/lib/templating/listShortcuts.js b/packages/gitbook/src/templating/listShortcuts.js
index 8d0a64a..5df88bb 100644
--- a/packages/gitbook/lib/templating/listShortcuts.js
+++ b/packages/gitbook/src/templating/listShortcuts.js
@@ -1,5 +1,5 @@
-var Immutable = require('immutable');
-var parsers = require('../parsers');
+const Immutable = require('immutable');
+const parsers = require('../parsers');
 
 /**
  * Return a list of all shortcuts that can apply
@@ -10,7 +10,7 @@ var parsers = require('../parsers');
  * @return {List<TemplateShortcut>}
  */
 function listShortcuts(blocks, filePath) {
-    var parser = parsers.getForFile(filePath);
+    const parser = parsers.getForFile(filePath);
 
     if (!parser) {
         return Immutable.List();
diff --git a/packages/gitbook/lib/templating/postRender.js b/packages/gitbook/src/templating/postRender.js
index f464f86..7fdfbf4 100644
--- a/packages/gitbook/lib/templating/postRender.js
+++ b/packages/gitbook/src/templating/postRender.js
@@ -1,4 +1,4 @@
-var Promise = require('../utils/promise');
+const Promise = require('../utils/promise');
 
 
 /**
@@ -9,10 +9,10 @@ var Promise = require('../utils/promise');
  * @return {Object} {blocks: Set, content: String}
  */
 function replaceBlocks(content, blocks) {
-    var newContent = content.replace(/\{\{\-\%([\s\S]+?)\%\-\}\}/g, function(match, key) {
-        var replacedWith = match;
+    const newContent = content.replace(/\{\{\-\%([\s\S]+?)\%\-\}\}/g, function(match, key) {
+        let replacedWith = match;
 
-        var block = blocks.get(key);
+        const block = blocks.get(key);
         if (block) {
             replacedWith = replaceBlocks(block.get('body'), blocks);
         }
@@ -33,13 +33,13 @@ function replaceBlocks(content, blocks) {
  * @return {Promise<String>}
  */
 function postRender(engine, output) {
-    var content = output.getContent();
-    var blocks = output.getBlocks();
+    const content = output.getContent();
+    const blocks = output.getBlocks();
 
-    var result = replaceBlocks(content, blocks);
+    const result = replaceBlocks(content, blocks);
 
     return Promise.forEach(blocks, function(block) {
-        var post = block.get('post');
+        const post = block.get('post');
 
         if (!post) {
             return;
diff --git a/packages/gitbook/lib/templating/render.js b/packages/gitbook/src/templating/render.js
index 1a8b0cd..53ed546 100644
--- a/packages/gitbook/lib/templating/render.js
+++ b/packages/gitbook/src/templating/render.js
@@ -1,7 +1,7 @@
-var Promise = require('../utils/promise');
-var timing = require('../utils/timing');
-var TemplateOutput = require('../models/templateOutput');
-var replaceShortcuts = require('./replaceShortcuts');
+const Promise = require('../utils/promise');
+const timing = require('../utils/timing');
+const TemplateOutput = require('../models/templateOutput');
+const replaceShortcuts = require('./replaceShortcuts');
 
 /**
  * Render a template
@@ -16,10 +16,10 @@ function renderTemplate(engine, filePath, content, context) {
     context = context || {};
 
     // Mutable objects to contains all blocks requiring post-processing
-    var blocks = {};
+    const blocks = {};
 
     // Create nunjucks environment
-    var env = engine.toNunjucks(blocks);
+    const env = engine.toNunjucks(blocks);
 
     // Replace shortcuts from plugin's blocks
     content = replaceShortcuts(engine.getBlocks(), filePath, content);
diff --git a/packages/gitbook/lib/templating/renderFile.js b/packages/gitbook/src/templating/renderFile.js
index 8672e8b..a2463f8 100644
--- a/packages/gitbook/lib/templating/renderFile.js
+++ b/packages/gitbook/src/templating/renderFile.js
@@ -1,6 +1,6 @@
-var Promise = require('../utils/promise');
-var error = require('../utils/error');
-var render = require('./render');
+const Promise = require('../utils/promise');
+const error = require('../utils/error');
+const render = require('./render');
 
 /**
  * Render a template
@@ -11,10 +11,10 @@ var render = require('./render');
  * @return {Promise<TemplateOutput>}
  */
 function renderTemplateFile(engine, filePath, context) {
-    var loader = engine.getLoader();
+    const loader = engine.getLoader();
 
     // Resolve the filePath
-    var resolvedFilePath = loader.resolve(null, filePath);
+    const resolvedFilePath = loader.resolve(null, filePath);
 
     return Promise()
     .then(function() {
@@ -22,7 +22,7 @@ function renderTemplateFile(engine, filePath, context) {
             return loader.getSource(resolvedFilePath);
         }
 
-        var deferred = Promise.defer();
+        const deferred = Promise.defer();
         loader.getSource(resolvedFilePath, deferred.makeNodeResolver());
         return deferred.promise;
     })
diff --git a/packages/gitbook/lib/templating/replaceShortcuts.js b/packages/gitbook/src/templating/replaceShortcuts.js
index 1cfdbf0..25f598f 100644
--- a/packages/gitbook/lib/templating/replaceShortcuts.js
+++ b/packages/gitbook/src/templating/replaceShortcuts.js
@@ -1,5 +1,5 @@
-var escapeStringRegexp = require('escape-string-regexp');
-var listShortcuts = require('./listShortcuts');
+const escapeStringRegexp = require('escape-string-regexp');
+const listShortcuts = require('./listShortcuts');
 
 /**
  * Apply a shortcut of block to a template
@@ -8,13 +8,13 @@ var listShortcuts = require('./listShortcuts');
  * @return {String}
  */
 function applyShortcut(content, shortcut) {
-    var start = shortcut.getStart();
-    var end = shortcut.getEnd();
+    const start = shortcut.getStart();
+    const end = shortcut.getEnd();
 
-    var tagStart = shortcut.getStartTag();
-    var tagEnd = shortcut.getEndTag();
+    const tagStart = shortcut.getStartTag();
+    const tagEnd = shortcut.getEndTag();
 
-    var regex = new RegExp(
+    const regex = new RegExp(
         escapeStringRegexp(start) + '([\\s\\S]*?[^\\$])' + escapeStringRegexp(end),
        'g'
     );
@@ -32,7 +32,7 @@ function applyShortcut(content, shortcut) {
  * @return {String}
  */
 function replaceShortcuts(blocks, filePath, content) {
-    var shortcuts = listShortcuts(blocks, filePath);
+    const shortcuts = listShortcuts(blocks, filePath);
     return shortcuts.reduce(applyShortcut, content);
 }
 
diff --git a/packages/gitbook/lib/templating/themesLoader.js b/packages/gitbook/src/templating/themesLoader.js
index bae4c12..b1639c5 100644
--- a/packages/gitbook/lib/templating/themesLoader.js
+++ b/packages/gitbook/src/templating/themesLoader.js
@@ -1,13 +1,13 @@
-var Immutable = require('immutable');
-var nunjucks = require('nunjucks');
-var fs = require('fs');
-var path = require('path');
+const Immutable = require('immutable');
+const nunjucks = require('nunjucks');
+const fs = require('fs');
+const path = require('path');
 
-var PathUtils = require('../utils/path');
+const PathUtils = require('../utils/path');
 
 
-var ThemesLoader = nunjucks.Loader.extend({
-    init: function(searchPaths) {
+const ThemesLoader = nunjucks.Loader.extend({
+    init(searchPaths) {
         this.searchPaths = Immutable.List(searchPaths)
             .map(path.normalize);
     },
@@ -17,24 +17,24 @@ var ThemesLoader = nunjucks.Loader.extend({
      * @param {String}
      * @return {Object}
      */
-    getSource: function(fullpath) {
+    getSource(fullpath) {
         if (!fullpath) return null;
 
         fullpath = this.resolve(null, fullpath);
-        var templateName = this.getTemplateName(fullpath);
+        const templateName = this.getTemplateName(fullpath);
 
-        if(!fullpath) {
+        if (!fullpath) {
             return null;
         }
 
-        var src = fs.readFileSync(fullpath, 'utf-8');
+        let src = fs.readFileSync(fullpath, 'utf-8');
 
         src = '{% do %}var template = template || {}; template.stack = template.stack || []; template.stack.push(template.self); template.self = ' + JSON.stringify(templateName) + '{% enddo %}\n' +
             src +
             '\n{% do %}template.self = template.stack.pop();{% enddo %}';
 
         return {
-            src: src,
+            src,
             path: fullpath,
             noCache: true
         };
@@ -44,7 +44,7 @@ var ThemesLoader = nunjucks.Loader.extend({
      * Nunjucks calls "isRelative" to determine when to call "resolve".
      * We handle absolute paths ourselves in ".resolve" so we always return true
      */
-    isRelative: function() {
+    isRelative() {
         return true;
     },
 
@@ -53,7 +53,7 @@ var ThemesLoader = nunjucks.Loader.extend({
      * @param {String} filepath
      * @return {String} searchPath
      */
-    getSearchPath: function(filepath) {
+    getSearchPath(filepath) {
         return this.searchPaths
             .sortBy(function(s) {
                 return -s.length;
@@ -68,9 +68,9 @@ var ThemesLoader = nunjucks.Loader.extend({
      * @param {String} filepath
      * @return {String} name
      */
-    getTemplateName: function(filepath) {
-        var originalSearchPath = this.getSearchPath(filepath);
-        return originalSearchPath? path.relative(originalSearchPath, filepath) : null;
+    getTemplateName(filepath) {
+        const originalSearchPath = this.getSearchPath(filepath);
+        return originalSearchPath ? path.relative(originalSearchPath, filepath) : null;
     },
 
     /**
@@ -79,8 +79,8 @@ var ThemesLoader = nunjucks.Loader.extend({
      * @param {String} to
      * @return {String|null}
      */
-    resolve: function(from, to) {
-        var searchPaths = this.searchPaths;
+    resolve(from, to) {
+        let searchPaths = this.searchPaths;
 
         // Relative template like "./test.html"
         if (PathUtils.isPureRelative(to) && from) {
@@ -88,19 +88,19 @@ var ThemesLoader = nunjucks.Loader.extend({
         }
 
         // Determine in which search folder we currently are
-        var originalSearchPath = this.getSearchPath(from);
-        var originalFilename = this.getTemplateName(from);
+        const originalSearchPath = this.getSearchPath(from);
+        const originalFilename = this.getTemplateName(from);
 
         // If we are including same file from a different search path
         // Slice the search paths to avoid including from previous ones
         if (originalFilename == to) {
-            var currentIndex = searchPaths.indexOf(originalSearchPath);
+            const currentIndex = searchPaths.indexOf(originalSearchPath);
             searchPaths = searchPaths.slice(currentIndex + 1);
         }
 
         // Absolute template to resolve in root folder
-        var resultFolder = searchPaths.find(function(basePath) {
-            var p = path.resolve(basePath, to);
+        const resultFolder = searchPaths.find(function(basePath) {
+            const p = path.resolve(basePath, to);
 
             return (
                 p.indexOf(basePath) === 0
diff --git a/packages/gitbook/lib/utils/__tests__/git.js b/packages/gitbook/src/utils/__tests__/git.js
index abc1ea1..445b8eb 100644
--- a/packages/gitbook/lib/utils/__tests__/git.js
+++ b/packages/gitbook/src/utils/__tests__/git.js
@@ -1,7 +1,7 @@
-var path = require('path');
-var os = require('os');
+const path = require('path');
+const os = require('os');
 
-var Git = require('../git');
+const Git = require('../git');
 
 describe('Git', function() {
 
@@ -20,7 +20,7 @@ describe('Git', function() {
         });
 
         it('should parse HTTPS urls', function() {
-            var parts = Git.parseUrl('git+https://gist.github.com/69ea4542e4c8967d2fa7.git/test.md');
+            const parts = Git.parseUrl('git+https://gist.github.com/69ea4542e4c8967d2fa7.git/test.md');
 
             expect(parts.host).toBe('https://gist.github.com/69ea4542e4c8967d2fa7.git');
             expect(parts.ref).toBe(null);
@@ -28,7 +28,7 @@ describe('Git', function() {
         });
 
         it('should parse HTTPS urls with a reference', function() {
-            var parts = Git.parseUrl('git+https://gist.github.com/69ea4542e4c8967d2fa7.git/test.md#1.0.0');
+            const parts = Git.parseUrl('git+https://gist.github.com/69ea4542e4c8967d2fa7.git/test.md#1.0.0');
 
             expect(parts.host).toBe('https://gist.github.com/69ea4542e4c8967d2fa7.git');
             expect(parts.ref).toBe('1.0.0');
@@ -36,7 +36,7 @@ describe('Git', function() {
         });
 
         it('should parse SSH urls', function() {
-            var parts = Git.parseUrl('git+git@github.com:GitbookIO/gitbook.git/directory/README.md#e1594cde2c32e4ff48f6c4eff3d3d461743d74e1');
+            const parts = Git.parseUrl('git+git@github.com:GitbookIO/gitbook.git/directory/README.md#e1594cde2c32e4ff48f6c4eff3d3d461743d74e1');
 
             expect(parts.host).toBe('git@github.com:GitbookIO/gitbook.git');
             expect(parts.ref).toBe('e1594cde2c32e4ff48f6c4eff3d3d461743d74e1');
@@ -46,7 +46,7 @@ describe('Git', function() {
 
     describe('Cloning and resolving', function() {
         it('should clone an HTTPS url', function() {
-            var git = new Git(path.join(os.tmpdir(), 'test-git-'+Date.now()));
+            const git = new Git(path.join(os.tmpdir(), 'test-git-' + Date.now()));
             return git.resolve('git+https://gist.github.com/69ea4542e4c8967d2fa7.git/test.md')
             .then(function(filename) {
                 expect(path.extname(filename)).toBe('.md');
diff --git a/packages/gitbook/lib/utils/__tests__/location.js b/packages/gitbook/src/utils/__tests__/location.js
index 822338e..a565adb 100644
--- a/packages/gitbook/lib/utils/__tests__/location.js
+++ b/packages/gitbook/src/utils/__tests__/location.js
@@ -1,4 +1,4 @@
-var LocationUtils = require('../location');
+const LocationUtils = require('../location');
 
 describe('LocationUtils', function() {
     it('should correctly test external location', function() {
@@ -97,4 +97,3 @@ describe('LocationUtils', function() {
 
 });
 
-
diff --git a/packages/gitbook/lib/utils/__tests__/path.js b/packages/gitbook/src/utils/__tests__/path.js
index 22bb016..1f8a1d3 100644
--- a/packages/gitbook/lib/utils/__tests__/path.js
+++ b/packages/gitbook/src/utils/__tests__/path.js
@@ -1,7 +1,7 @@
-var path = require('path');
+const path = require('path');
 
 describe('Paths', function() {
-    var PathUtils = require('..//path');
+    const PathUtils = require('..//path');
 
     describe('setExtension', function() {
         it('should correctly change extension of filename', function() {
diff --git a/packages/gitbook/lib/utils/command.js b/packages/gitbook/src/utils/command.js
index 90a556e..efa9699 100644
--- a/packages/gitbook/lib/utils/command.js
+++ b/packages/gitbook/src/utils/command.js
@@ -1,7 +1,7 @@
-var is = require('is');
-var childProcess = require('child_process');
-var spawn = require('spawn-cmd').spawn;
-var Promise = require('./promise');
+const is = require('is');
+const childProcess = require('child_process');
+const spawn = require('spawn-cmd').spawn;
+const Promise = require('./promise');
 
 /**
     Execute a command
@@ -11,9 +11,9 @@ var Promise = require('./promise');
     @return {Promise}
 */
 function exec(command, options) {
-    var d = Promise.defer();
+    const d = Promise.defer();
 
-    var child = childProcess.exec(command, options, function(err, stdout, stderr) {
+    const child = childProcess.exec(command, options, function(err, stdout, stderr) {
         if (!err) {
             return d.resolve();
         }
@@ -22,11 +22,11 @@ function exec(command, options) {
         d.reject(err);
     });
 
-    child.stdout.on('data', function (data) {
+    child.stdout.on('data', function(data) {
         d.notify(data);
     });
 
-    child.stderr.on('data', function (data) {
+    child.stderr.on('data', function(data) {
         d.notify(data);
     });
 
@@ -42,18 +42,18 @@ function exec(command, options) {
     @return {Promise}
 */
 function spawnCmd(command, args, options) {
-    var d = Promise.defer();
-    var child = spawn(command, args, options);
+    const d = Promise.defer();
+    const child = spawn(command, args, options);
 
     child.on('error', function(error) {
         return d.reject(error);
     });
 
-    child.stdout.on('data', function (data) {
+    child.stdout.on('data', function(data) {
         d.notify(data);
     });
 
-    child.stderr.on('data', function (data) {
+    child.stderr.on('data', function(data) {
         d.notify(data);
     });
 
@@ -61,7 +61,7 @@ function spawnCmd(command, args, options) {
         if (code === 0) {
             d.resolve();
         } else {
-            d.reject(new Error('Error with command "'+command+'"'));
+            d.reject(new Error('Error with command "' + command + '"'));
         }
     });
 
@@ -92,10 +92,10 @@ function escapeShellArg(value) {
     @return {String}
 */
 function optionsToShellArgs(options) {
-    var result = [];
+    const result = [];
 
-    for (var key in options) {
-        var value = options[key];
+    for (const key in options) {
+        const value = options[key];
 
         if (value === null || value === undefined || value === false) {
             continue;
@@ -112,7 +112,7 @@ function optionsToShellArgs(options) {
 }
 
 module.exports = {
-    exec: exec,
+    exec,
     spawn: spawnCmd,
-    optionsToShellArgs: optionsToShellArgs
+    optionsToShellArgs
 };
diff --git a/packages/gitbook/lib/utils/error.js b/packages/gitbook/src/utils/error.js
index 7686779..925b5ff 100644
--- a/packages/gitbook/lib/utils/error.js
+++ b/packages/gitbook/src/utils/error.js
@@ -1,7 +1,7 @@
-var is = require('is');
+const is = require('is');
 
-var TypedError = require('error/typed');
-var WrappedError = require('error/wrapped');
+const TypedError = require('error/typed');
+const WrappedError = require('error/wrapped');
 
 
 // Enforce as an Error object, and cleanup message
@@ -13,31 +13,31 @@ function enforce(err) {
 }
 
 // Random error wrappers during parsing/generation
-var ParsingError = WrappedError({
+const ParsingError = WrappedError({
     message: 'Parsing Error: {origMessage}',
     type: 'parse'
 });
-var OutputError = WrappedError({
+const OutputError = WrappedError({
     message: 'Output Error: {origMessage}',
     type: 'generate'
 });
 
 // A file does not exists
-var FileNotFoundError = TypedError({
+const FileNotFoundError = TypedError({
     type: 'file.not-found',
     message: 'No "{filename}" file (or is ignored)',
     filename: null
 });
 
 // A file cannot be parsed
-var FileNotParsableError = TypedError({
+const FileNotParsableError = TypedError({
     type: 'file.not-parsable',
     message: '"{filename}" file cannot be parsed',
     filename: null
 });
 
 // A file is outside the scope
-var FileOutOfScopeError = TypedError({
+const FileOutOfScopeError = TypedError({
     type: 'file.out-of-scope',
     message: '"{filename}" not in "{root}"',
     filename: null,
@@ -46,7 +46,7 @@ var FileOutOfScopeError = TypedError({
 });
 
 // A file is outside the scope
-var RequireInstallError = TypedError({
+const RequireInstallError = TypedError({
     type: 'install.required',
     message: '"{cmd}" is not installed.\n{install}',
     cmd: null,
@@ -55,45 +55,45 @@ var RequireInstallError = TypedError({
 });
 
 // Error for nunjucks templates
-var TemplateError = WrappedError({
+const TemplateError = WrappedError({
     message: 'Error compiling template "{filename}": {origMessage}',
     type: 'template',
     filename: null
 });
 
 // Error for nunjucks templates
-var PluginError = WrappedError({
+const PluginError = WrappedError({
     message: 'Error with plugin "{plugin}": {origMessage}',
     type: 'plugin',
     plugin: null
 });
 
 // Error with the book's configuration
-var ConfigurationError = WrappedError({
+const ConfigurationError = WrappedError({
     message: 'Error with book\'s configuration: {origMessage}',
     type: 'configuration'
 });
 
 // Error during ebook generation
-var EbookError = WrappedError({
+const EbookError = WrappedError({
     message: 'Error during ebook generation: {origMessage}\n{stdout}',
     type: 'ebook',
     stdout: ''
 });
 
 module.exports = {
-    enforce: enforce,
+    enforce,
 
-    ParsingError: ParsingError,
-    OutputError: OutputError,
-    RequireInstallError: RequireInstallError,
+    ParsingError,
+    OutputError,
+    RequireInstallError,
 
-    FileNotParsableError: FileNotParsableError,
-    FileNotFoundError: FileNotFoundError,
-    FileOutOfScopeError: FileOutOfScopeError,
+    FileNotParsableError,
+    FileNotFoundError,
+    FileOutOfScopeError,
 
-    TemplateError: TemplateError,
-    PluginError: PluginError,
-    ConfigurationError: ConfigurationError,
-    EbookError: EbookError
+    TemplateError,
+    PluginError,
+    ConfigurationError,
+    EbookError
 };
diff --git a/packages/gitbook/lib/utils/fs.js b/packages/gitbook/src/utils/fs.js
index 35839a3..17b2ebb 100644
--- a/packages/gitbook/lib/utils/fs.js
+++ b/packages/gitbook/src/utils/fs.js
@@ -1,30 +1,30 @@
-var fs = require('graceful-fs');
-var mkdirp = require('mkdirp');
-var destroy = require('destroy');
-var rmdir = require('rmdir');
-var tmp = require('tmp');
-var request = require('request');
-var path = require('path');
-var cp = require('cp');
-var cpr = require('cpr');
-
-var Promise = require('./promise');
+const fs = require('graceful-fs');
+const mkdirp = require('mkdirp');
+const destroy = require('destroy');
+const rmdir = require('rmdir');
+const tmp = require('tmp');
+const request = require('request');
+const path = require('path');
+const cp = require('cp');
+const cpr = require('cpr');
+
+const Promise = require('./promise');
 
 // Write a stream to a file
 function writeStream(filename, st) {
-    var d = Promise.defer();
+    const d = Promise.defer();
 
-    var wstream = fs.createWriteStream(filename);
-    var cleanup = function() {
+    const wstream = fs.createWriteStream(filename);
+    const cleanup = function() {
         destroy(wstream);
         wstream.removeAllListeners();
     };
 
-    wstream.on('finish', function () {
+    wstream.on('finish', function() {
         cleanup();
         d.resolve();
     });
-    wstream.on('error', function (err) {
+    wstream.on('error', function(err) {
         cleanup();
         d.reject(err);
     });
@@ -41,7 +41,7 @@ function writeStream(filename, st) {
 
 // Return a promise resolved with a boolean
 function fileExists(filename) {
-    var d = Promise.defer();
+    const d = Promise.defer();
 
     fs.exists(filename, function(exists) {
         d.resolve(exists);
@@ -69,13 +69,13 @@ function download(uri, dest) {
 
 // Find a filename available in a folder
 function uniqueFilename(base, filename) {
-    var ext = path.extname(filename);
+    const ext = path.extname(filename);
     filename = path.resolve(base, filename);
     filename = path.join(path.dirname(filename), path.basename(filename, ext));
 
-    var _filename = filename+ext;
+    let _filename = filename + ext;
 
-    var i = 0;
+    let i = 0;
     while (fs.existsSync(filename)) {
         _filename = filename + '_' + i + ext;
         i = i + 1;
@@ -86,14 +86,14 @@ function uniqueFilename(base, filename) {
 
 // Create all required folder to create a file
 function ensureFile(filename) {
-    var base = path.dirname(filename);
+    const base = path.dirname(filename);
     return Promise.nfcall(mkdirp, base);
 }
 
 // Remove a folder
 function rmDir(base) {
     return Promise.nfcall(rmdir, base, {
-        fs: fs
+        fs
     });
 }
 
@@ -121,7 +121,7 @@ function assertFile(filePath, generator) {
     @return {String}
 */
 function pickFile(rootFolder, fileName) {
-    var result = path.join(rootFolder, fileName);
+    const result = path.join(rootFolder, fileName);
     if (fs.existsSync(result)) {
         return result;
     }
@@ -151,20 +151,20 @@ module.exports = {
     mkdirp: Promise.nfbind(mkdirp),
     readFile: Promise.nfbind(fs.readFile),
     writeFile: Promise.nfbind(fs.writeFile),
-    assertFile: assertFile,
-    pickFile: pickFile,
+    assertFile,
+    pickFile,
     stat: Promise.nfbind(fs.stat),
     statSync: fs.statSync,
     readdir: Promise.nfbind(fs.readdir),
-    writeStream: writeStream,
+    writeStream,
     readStream: fs.createReadStream,
     copy: Promise.nfbind(cp),
     copyDir: Promise.nfbind(cpr),
     tmpFile: genTmpFile,
     tmpDir: genTmpDir,
-    download: download,
-    uniqueFilename: uniqueFilename,
-    ensureFile: ensureFile,
-    ensureFolder: ensureFolder,
-    rmDir: rmDir
+    download,
+    uniqueFilename,
+    ensureFile,
+    ensureFolder,
+    rmDir
 };
diff --git a/packages/gitbook/lib/utils/genKey.js b/packages/gitbook/src/utils/genKey.js
index 0650011..e4982f4 100644
--- a/packages/gitbook/lib/utils/genKey.js
+++ b/packages/gitbook/src/utils/genKey.js
@@ -1,4 +1,4 @@
-var lastKey = 0;
+let lastKey = 0;
 
 /*
     Generate a random key
@@ -6,7 +6,7 @@ var lastKey = 0;
 */
 function generateKey() {
     lastKey += 1;
-    var str = lastKey.toString(16);
+    const str = lastKey.toString(16);
     return '00000'.slice(str.length) + str;
 }
 
diff --git a/packages/gitbook/src/utils/git.js b/packages/gitbook/src/utils/git.js
new file mode 100644
index 0000000..8ec23dd
--- /dev/null
+++ b/packages/gitbook/src/utils/git.js
@@ -0,0 +1,135 @@
+const is = require('is');
+const path = require('path');
+const crc = require('crc');
+const URI = require('urijs');
+
+const pathUtil = require('./path');
+const Promise = require('./promise');
+const command = require('./command');
+const fs = require('./fs');
+
+const GIT_PREFIX = 'git+';
+
+class Git {
+    constructor() {
+        this.tmpDir = null;
+        this.cloned = {};
+    }
+
+    // Return an unique ID for a combinaison host/ref
+    repoID(host, ref) {
+        return crc.crc32(host + '#' + (ref || '')).toString(16);
+    }
+
+    // Allocate a temporary folder for cloning repos in it
+    allocateDir() {
+        const that = this;
+
+        if (this.tmpDir) return Promise();
+
+        return fs.tmpDir()
+        .then(function(dir) {
+            that.tmpDir = dir;
+        });
+    }
+
+    // Clone a git repository if non existant
+    clone(host, ref) {
+        const that = this;
+
+        return this.allocateDir()
+
+        // Return or clone the git repo
+        .then(function() {
+            // Unique ID for repo/ref combinaison
+            const repoId = that.repoID(host, ref);
+
+            // Absolute path to the folder
+            const repoPath = path.join(that.tmpDir, repoId);
+
+            if (that.cloned[repoId]) return repoPath;
+
+            // Clone repo
+            return command.exec('git clone ' + host + ' ' + repoPath)
+
+            // Checkout reference if specified
+            .then(function() {
+                that.cloned[repoId] = true;
+
+                if (!ref) return;
+                return command.exec('git checkout ' + ref, { cwd: repoPath });
+            })
+            .thenResolve(repoPath);
+        });
+    }
+
+    // Get file from a git repo
+    resolve(giturl) {
+        // Path to a file in a git repo?
+        if (!Git.isUrl(giturl)) {
+            if (this.resolveRoot(giturl)) return Promise(giturl);
+            return Promise(null);
+        }
+        if (is.string(giturl)) giturl = Git.parseUrl(giturl);
+        if (!giturl) return Promise(null);
+
+        // Clone or get from cache
+        return this.clone(giturl.host, giturl.ref)
+        .then(function(repo) {
+            return path.resolve(repo, giturl.filepath);
+        });
+    }
+
+    // Return root of git repo from a filepath
+    resolveRoot(filepath) {
+        // No git repo cloned, or file is not in a git repository
+        if (!this.tmpDir || !pathUtil.isInRoot(this.tmpDir, filepath)) return null;
+
+        // Extract first directory (is the repo id)
+        const relativeToGit = path.relative(this.tmpDir, filepath);
+        const repoId = relativeToGit.split(path.sep)[0];
+
+        if (!repoId) {
+            return;
+        }
+
+        // Return an absolute file
+        return path.resolve(this.tmpDir, repoId);
+    }
+
+    // Check if an url is a git dependency url
+    static isUrl(giturl) {
+        return (giturl.indexOf(GIT_PREFIX) === 0);
+    }
+
+    // Parse and extract infos
+    static parseUrl(giturl) {
+        if (!Git.isUrl(giturl)) {
+            return null;
+        }
+        giturl = giturl.slice(GIT_PREFIX.length);
+
+        const uri = new URI(giturl);
+        const ref = uri.fragment() || null;
+        uri.fragment(null);
+
+        // Extract file inside the repo (after the .git)
+        const fileParts = uri.path().split('.git');
+        let filepath = fileParts.length > 1 ? fileParts.slice(1).join('.git') : '';
+        if (filepath[0] == '/') {
+            filepath = filepath.slice(1);
+        }
+
+        // Recreate pathname without the real filename
+        uri.path(fileParts[0] + '.git');
+
+        return {
+            host: uri.toString(),
+            ref,
+            filepath
+        };
+    }
+
+}
+
+module.exports = Git;
diff --git a/packages/gitbook/lib/utils/images.js b/packages/gitbook/src/utils/images.js
index 6d4b927..808be63 100644
--- a/packages/gitbook/lib/utils/images.js
+++ b/packages/gitbook/src/utils/images.js
@@ -1,7 +1,7 @@
-var Promise = require('./promise');
-var command = require('./command');
-var fs = require('./fs');
-var error = require('./error');
+const Promise = require('./promise');
+const command = require('./command');
+const fs = require('./fs');
+const error = require('./error');
 
 // Convert a svg file to a pmg
 function convertSVGToPNG(source, dest, options) {
@@ -20,7 +20,7 @@ function convertSVGToPNG(source, dest, options) {
     .then(function() {
         if (fs.existsSync(dest)) return;
 
-        throw new Error('Error converting '+source+' into '+dest);
+        throw new Error('Error converting ' + source + ' into ' + dest);
     });
 }
 
@@ -42,19 +42,19 @@ function convertSVGBufferToPNG(buf, dest) {
 function convertInlinePNG(source, dest) {
     if (!/^data\:image\/png/.test(source)) return Promise.reject(new Error('Source is not a PNG data-uri'));
 
-    var base64data = source.split('data:image/png;base64,')[1];
-    var buf = new Buffer(base64data, 'base64');
+    const base64data = source.split('data:image/png;base64,')[1];
+    const buf = new Buffer(base64data, 'base64');
 
     return fs.writeFile(dest, buf)
     .then(function() {
         if (fs.existsSync(dest)) return;
 
-        throw new Error('Error converting '+source+' into '+dest);
+        throw new Error('Error converting ' + source + ' into ' + dest);
     });
 }
 
 module.exports = {
-    convertSVGToPNG: convertSVGToPNG,
-    convertSVGBufferToPNG: convertSVGBufferToPNG,
-    convertInlinePNG: convertInlinePNG
-};
\ No newline at end of file
+    convertSVGToPNG,
+    convertSVGBufferToPNG,
+    convertInlinePNG
+};
diff --git a/packages/gitbook/lib/utils/location.js b/packages/gitbook/src/utils/location.js
index 00d8004..6dc41ba 100644
--- a/packages/gitbook/lib/utils/location.js
+++ b/packages/gitbook/src/utils/location.js
@@ -1,11 +1,11 @@
-var url = require('url');
-var path = require('path');
+const url = require('url');
+const path = require('path');
 
 // Is the url an external url
 function isExternal(href) {
     try {
         return Boolean(url.parse(href).protocol) && !isDataURI(href);
-    } catch(err) {
+    } catch (err) {
         return false;
     }
 }
@@ -14,7 +14,7 @@ function isExternal(href) {
 function isDataURI(href) {
     try {
         return Boolean(url.parse(href).protocol) && (url.parse(href).protocol === 'data:');
-    } catch(err) {
+    } catch (err) {
         return false;
     }
 }
@@ -27,9 +27,9 @@ function isRelative(href) {
 // Return true if the link is an achor
 function isAnchor(href) {
     try {
-        var parsed = url.parse(href);
+        const parsed = url.parse(href);
         return !!(!parsed.protocol && !parsed.path && parsed.hash);
-    } catch(err) {
+    } catch (err) {
         return false;
     }
 }
@@ -67,14 +67,14 @@ function toAbsolute(_href, dir, outdir) {
         return _href;
     }
 
-    outdir = outdir == undefined? dir : outdir;
+    outdir = outdir == undefined ? dir : outdir;
 
     _href = normalize(_href);
     dir = normalize(dir);
     outdir = normalize(outdir);
 
     // Path "_href" inside the base folder
-    var hrefInRoot = normalize(path.join(dir, _href));
+    let hrefInRoot = normalize(path.join(dir, _href));
     if (_href[0] == '/') {
         hrefInRoot = normalize(_href.slice(1));
     }
@@ -97,8 +97,8 @@ function toAbsolute(_href, dir, outdir) {
  * @return {String}
  */
 function relative(dir, file) {
-    var isDirectory = file.slice(-1) === '/';
-    return normalize(path.relative(dir, file)) + (isDirectory? '/': '');
+    const isDirectory = file.slice(-1) === '/';
+    return normalize(path.relative(dir, file)) + (isDirectory ? '/' : '');
 }
 
 /**
@@ -126,14 +126,14 @@ function areIdenticalPaths(p1, p2) {
 }
 
 module.exports = {
-    areIdenticalPaths: areIdenticalPaths,
-    isDataURI:         isDataURI,
-    isExternal:        isExternal,
-    isRelative:        isRelative,
-    isAnchor:          isAnchor,
-    normalize:         normalize,
-    toAbsolute:        toAbsolute,
-    relative:          relative,
-    relativeForFile:   relativeForFile,
-    flatten:           flatten
+    areIdenticalPaths,
+    isDataURI,
+    isExternal,
+    isRelative,
+    isAnchor,
+    normalize,
+    toAbsolute,
+    relative,
+    relativeForFile,
+    flatten
 };
diff --git a/packages/gitbook/lib/utils/logger.js b/packages/gitbook/src/utils/logger.js
index 6fac92b..25f8517 100644
--- a/packages/gitbook/lib/utils/logger.js
+++ b/packages/gitbook/src/utils/logger.js
@@ -1,9 +1,9 @@
-var is = require('is');
-var util = require('util');
-var color = require('bash-color');
-var Immutable = require('immutable');
+const is = require('is');
+const util = require('util');
+const color = require('bash-color');
+const Immutable = require('immutable');
 
-var LEVELS = Immutable.Map({
+const LEVELS = Immutable.Map({
     DEBUG: 0,
     INFO: 1,
     WARN: 2,
@@ -11,7 +11,7 @@ var LEVELS = Immutable.Map({
     DISABLED: 10
 });
 
-var COLORS = Immutable.Map({
+const COLORS = Immutable.Map({
     DEBUG: color.purple,
     INFO: color.cyan,
     WARN: color.yellow,
@@ -22,7 +22,7 @@ function Logger(write, logLevel) {
     if (!(this instanceof Logger)) return new Logger(write, logLevel);
 
     this._write = write || function(msg) {
-        if(process.stdout) {
+        if (process.stdout) {
             process.stdout.write(msg);
         }
     };
@@ -82,8 +82,8 @@ Logger.prototype.write = function(msg) {
 /**
     Format a string using the first argument as a printf-like format.
 */
-Logger.prototype.format = function() {
-    return util.format.apply(util, arguments);
+Logger.prototype.format = function(...args) {
+    return util.format(...args);
 };
 
 /**
@@ -92,7 +92,7 @@ Logger.prototype.format = function() {
     @param {String}
 */
 Logger.prototype.writeLn = function(msg) {
-    return this.write((msg || '')+'\n');
+    return this.write((msg || '') + '\n');
 };
 
 /**
@@ -100,17 +100,16 @@ Logger.prototype.writeLn = function(msg) {
 
     @param {Number} level
 */
-Logger.prototype.log = function(level) {
+Logger.prototype.log = function(level, ...args) {
     if (level < this.logLevel) return;
 
-    var levelKey = LEVELS.findKey(function(v) {
+    const levelKey = LEVELS.findKey(function(v) {
         return v === level;
     });
-    var args = Array.prototype.slice.apply(arguments, [1]);
-    var msg = this.format.apply(this, args);
+    let msg = this.format(...args);
 
     if (this.lastChar == '\n') {
-        msg = COLORS.get(levelKey)(levelKey.toLowerCase()+':')+' '+msg;
+        msg = COLORS.get(levelKey)(levelKey.toLowerCase() + ':') + ' ' + msg;
     }
 
     return this.write(msg);
@@ -119,21 +118,20 @@ Logger.prototype.log = function(level) {
 /**
     Log/Print a line if level is allowed
 */
-Logger.prototype.logLn = function() {
+Logger.prototype.logLn = function(...args) {
     if (this.lastChar != '\n') this.write('\n');
 
-    var args = Array.prototype.slice.apply(arguments);
     args.push('\n');
-    return this.log.apply(this, args);
+    return this.log(...args);
 };
 
 /**
     Log a confirmation [OK]
 */
-Logger.prototype.ok = function(level) {
-    var args = Array.prototype.slice.apply(arguments, [1]);
-    var msg = this.format.apply(this, args);
-    if (arguments.length > 1) {
+Logger.prototype.ok = function(level, ...args) {
+    const msg = this.format(...args);
+
+    if (args.length > 0) {
         this.logLn(level, color.green('>> ') + msg.trim().replace(/\n/g, color.green('\n>> ')));
     } else {
         this.log(level, color.green('OK'), '\n');
@@ -155,10 +153,10 @@ Logger.prototype.fail = function(level) {
     @return {Promise}
 */
 Logger.prototype.promise = function(level, p) {
-    var that = this;
+    const that = this;
 
-    return p.
-    then(function(st) {
+    return p
+    .then(function(st) {
         that.ok(level);
         return st;
     }, function(err) {
diff --git a/packages/gitbook/lib/utils/mergeDefaults.js b/packages/gitbook/src/utils/mergeDefaults.js
index 47a374b..b2e8c3d 100644
--- a/packages/gitbook/lib/utils/mergeDefaults.js
+++ b/packages/gitbook/src/utils/mergeDefaults.js
@@ -1,4 +1,4 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
 /**
  * Merge
@@ -7,8 +7,8 @@ var Immutable = require('immutable');
  * @return {Object}
  */
 function mergeDefaults(obj, src) {
-    var objValue = Immutable.fromJS(obj);
-    var srcValue = Immutable.fromJS(src);
+    const objValue = Immutable.fromJS(obj);
+    const srcValue = Immutable.fromJS(src);
 
     return srcValue.mergeDeep(objValue).toJS();
 }
diff --git a/packages/gitbook/lib/utils/path.js b/packages/gitbook/src/utils/path.js
index 26b6005..01c2cbf 100644
--- a/packages/gitbook/lib/utils/path.js
+++ b/packages/gitbook/src/utils/path.js
@@ -1,5 +1,5 @@
-var path = require('path');
-var error = require('./error');
+const path = require('path');
+const error = require('./error');
 
 // Normalize a filename
 function normalizePath(filename) {
@@ -23,24 +23,21 @@ function isInRoot(root, filename) {
 
 // Resolve paths in a specific folder
 // Throw error if file is outside this folder
-function resolveInRoot(root) {
-    var input, result;
-    var args = Array.prototype.slice.call(arguments, 1);
-
-    input = args
+function resolveInRoot(root, ...args) {
+    const input = args
         .reduce(function(current, p) {
             // Handle path relative to book root ("/README.md")
             if (p[0] == '/' || p[0] == '\\') return p.slice(1);
 
-            return current? path.join(current, p) : path.normalize(p);
+            return current ? path.join(current, p) : path.normalize(p);
         }, '');
 
-    result = path.resolve(root, input);
+    const result = path.resolve(root, input);
 
     if (!isInRoot(root, result)) {
         throw new error.FileOutOfScopeError({
             filename: result,
-            root: root
+            root
         });
     }
 
@@ -66,9 +63,9 @@ function isPureRelative(filename) {
 }
 
 module.exports = {
-    isInRoot: isInRoot,
-    resolveInRoot: resolveInRoot,
+    isInRoot,
+    resolveInRoot,
     normalize: normalizePath,
-    setExtension: setExtension,
-    isPureRelative: isPureRelative
+    setExtension,
+    isPureRelative
 };
diff --git a/packages/gitbook/lib/utils/promise.js b/packages/gitbook/src/utils/promise.js
index b5cca4b..8cbbd47 100644
--- a/packages/gitbook/lib/utils/promise.js
+++ b/packages/gitbook/src/utils/promise.js
@@ -1,5 +1,5 @@
-var Q = require('q');
-var Immutable = require('immutable');
+const Q = require('q');
+const Immutable = require('immutable');
 
 // Debugging for long stack traces
 if (process.env.DEBUG || process.env.CI) {
@@ -14,7 +14,7 @@ if (process.env.DEBUG || process.env.CI) {
  * @return {Promise<Mixed>}
  */
 function reduce(arr, iter, base) {
-    arr = Immutable.Iterable.isIterable(arr)? arr : Immutable.List(arr);
+    arr = Immutable.Iterable.isIterable(arr) ? arr : Immutable.List(arr);
 
     return arr.reduce(function(prev, elem, key) {
         return prev
@@ -99,7 +99,7 @@ function mapAsList(arr, iter) {
  */
 function map(arr, iter) {
     if (Immutable.Map.isMap(arr)) {
-        var type = 'Map';
+        let type = 'Map';
         if (Immutable.OrderedMap.isOrderedMap(arr)) {
             type = 'OrderedMap';
         }
@@ -129,12 +129,10 @@ function map(arr, iter) {
  * @return {Funciton}
  */
 function wrap(func) {
-    return function() {
-        var args = Array.prototype.slice.call(arguments, 0);
-
+    return function(...args) {
         return Q()
         .then(function() {
-            return func.apply(null, args);
+            return func(...args);
         });
     };
 }
diff --git a/packages/gitbook/lib/utils/reducedObject.js b/packages/gitbook/src/utils/reducedObject.js
index 7bcfd5b..196a72c 100644
--- a/packages/gitbook/lib/utils/reducedObject.js
+++ b/packages/gitbook/src/utils/reducedObject.js
@@ -1,4 +1,4 @@
-var Immutable = require('immutable');
+const Immutable = require('immutable');
 
 /**
  *  Reduce the difference between a map and its default version
@@ -7,15 +7,15 @@ var Immutable = require('immutable');
  *  @return {Map} The properties of currentVersion that differs from defaultVersion
  */
 function reducedObject(defaultVersion, currentVersion) {
-    if(defaultVersion === undefined) {
+    if (defaultVersion === undefined) {
         return currentVersion;
     }
 
     return currentVersion.reduce(function(result, value, key) {
-        var defaultValue = defaultVersion.get(key);
+        const defaultValue = defaultVersion.get(key);
 
         if (Immutable.Map.isMap(value)) {
-            var diffs = reducedObject(defaultValue, value);
+            const diffs = reducedObject(defaultValue, value);
 
             if (diffs.size > 0) {
                 return result.set(key, diffs);
diff --git a/packages/gitbook/lib/utils/timing.js b/packages/gitbook/src/utils/timing.js
index e6b0323..1dce2a1 100644
--- a/packages/gitbook/lib/utils/timing.js
+++ b/packages/gitbook/src/utils/timing.js
@@ -1,8 +1,8 @@
-var Immutable = require('immutable');
-var is = require('is');
+const Immutable = require('immutable');
+const is = require('is');
 
-var timers = {};
-var startDate = Date.now();
+const timers = {};
+const startDate = Date.now();
 
 /**
     Mesure an operation
@@ -13,19 +13,19 @@ var startDate = Date.now();
 */
 function measure(type, p) {
     timers[type] = timers[type] || {
-        type: type,
+        type,
         count: 0,
         total: 0,
         min: undefined,
         max: 0
     };
 
-    var start = Date.now();
+    const start = Date.now();
 
     return p
     .fin(function() {
-        var end = Date.now();
-        var duration = (end - start);
+        const end = Date.now();
+        const duration = (end - start);
 
         timers[type].count ++;
         timers[type].total += duration;
@@ -51,7 +51,7 @@ function time(ms) {
         return (ms.toFixed(0)) + 'ms';
     }
 
-    return (ms/1000).toFixed(2) + 's';
+    return (ms / 1000).toFixed(2) + 's';
 }
 
 /**
@@ -60,12 +60,12 @@ function time(ms) {
     @param {Logger} logger
 */
 function dump(logger) {
-    var prefix = '    > ';
-    var measured = 0;
-    var totalDuration = Date.now() - startDate;
+    const prefix = '    > ';
+    let measured = 0;
+    const totalDuration = Date.now() - startDate;
 
     // Enable debug logging
-    var logLevel = logger.getLevel();
+    const logLevel = logger.getLevel();
     logger.setLevel('debug');
 
     Immutable.Map(timers)
@@ -75,11 +75,11 @@ function dump(logger) {
             return timer.total;
         })
         .forEach(function(timer) {
-            var percent = (timer.total * 100) / totalDuration;
+            const percent = (timer.total * 100) / totalDuration;
 
 
             logger.debug.ln((percent.toFixed(1)) + '% of time spent in "' + timer.type + '" (' + timer.count + ' times) :');
-            logger.debug.ln(prefix + 'Total: ' + time(timer.total)+ ' | Average: ' + time(timer.total / timer.count));
+            logger.debug.ln(prefix + 'Total: ' + time(timer.total) + ' | Average: ' + time(timer.total / timer.count));
             logger.debug.ln(prefix + 'Min: ' + time(timer.min) + ' | Max: ' + time(timer.max));
             logger.debug.ln('---------------------------');
         });
@@ -92,6 +92,6 @@ function dump(logger) {
 }
 
 module.exports = {
-    measure: measure,
-    dump: dump
+    measure,
+    dump
 };